Helicopter Flying Handbook
2012
U.S. Department of Transportation
FEDERAL AVIATION ADMINISTRATION
Flight Standards Service
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Preface
The Helicopter Flying Handbook is designed as a technical manual for applicants who are preparing for their private,
commercial, or flight instructor pilot certificates with a helicopter class rating. Certificated flight instructors may find
this handbook a valuable training aid, since detailed coverage of aerodynamics, flight controls, systems, performance,
flight maneuvers, emergencies, and aeronautical decision-making is included. Topics such as weather, navigation, radio
navigation and communications, use of flight information publications, and regulations are available in other Federal
Aviation Administration (FAA) publications.
This handbook conforms to pilot training and certification concepts established by the FAA. There are different ways of
teaching, as well as performing, flight procedures and maneuvers, and many variations in the explanations of aerodynamic
theories and principles. This handbook adopts a selective method and concept to flying helicopters. The discussion and
explanations reflect the most commonly used practices and principles. Occasionally the word “must” or similar language
is used where the desired action is deemed critical. The use of such language is not intended to add to, interpret, or relieve
a duty imposed by Title 14 of the Code of Federal Regulations (14 CFR). Persons working towards a helicopter rating are
advised to review the references from the applicable practical test standards (FAA-S-8081-3 for recreational applicants,
FAA-S-8081-15 for private applicants, and FAA-S-8081-16 for commercial applicants). Resources for study include
FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge, and FAA-H-8083-1, Aircraft Weight and Balance Handbook,
as these documents contain basic material not duplicated herein. All beginning applicants should refer to FAA-H-8083-25,
Pilot’s Handbook of Aeronautical Knowledge, for study and basic library reference.
It is essential for persons using this handbook to become familiar with and apply the pertinent parts of 14 CFR and the
Aeronautical Information Manual (AIM). The AIM is available online at www.faa.gov. The current Flight Standards
Service airman training and testing material and learning statements for all airman certificates and ratings can be obtained
from www.faa.gov.
This handbook supersedes FAA-H-8083-21, Rotorcraft Flying Handbook, dated 2000. Gyroplane information can be found
in the FAA-H-8083-16, Gyroplane Flying Handbook.
This handbook is available for download, in PDF format, from www.faa.gov.
This handbook is published by the United States Department of Transportation, Federal Aviation Administration, Airman
Testing Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125.
Comments regarding this publication should be sent, in email form, to the following address:
AFS630comments@faa.gov
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Acknowledgments
The Helicopter Flying Handbook was produced by the Federal Aviation Administration (FAA) with the assistance of Safety
Research Corporation of America (SRCA). The FAA wishes to acknowledge the following contributors:
Federation of American Scientists (www.fas.org) for rotor system content used in Chapter 5
Kaman Aerospace, Helicopters Division for image of Kaman used in Chapter 5
Burkhard Domke (www.b-domke.de) for images of rotor systems (Chapters 1 and 4)
New Zealand Civil Aviation Authority for image of safety procedures for approaching a helicopter (Chapter 9)
Shawn Coyle of Eagle Eye Solutions, LLC for images and content used in Chapter 10
Dr. Pat Veillette for information used on decision-making (Chapter 15)
Additional appreciation is extended to the Helicopter Association International (HAI), Aircraft Owners and Pilots Association
(AOPA), and the AOPA Air Safety Foundation for their technical support and input.
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Table of Contents
Preface....................................................................iii
Acknowledgments...................................................v
Table of Contents..................................................vii
Chapter 1
Introduction to the Helicopter.............................1-1
Introduction.....................................................................1-1
Uses.................................................................................1-3
Rotor System...................................................................1-3
Rotor Configurations...................................................1-4
Tail Rotor....................................................................1-5
Controlling Flight...........................................................1-5
Flight Conditions............................................................1-6
Chapter 2
Aerodynamics of Flight........................................2-1
Introduction.....................................................................2-1
Forces Acting on the Aircraft.........................................2-2
Lift...................................................................................2-2
Bernoulli’s Principle...................................................2-3
Venturi Flow...............................................................2-3
Newton’s Third Law of Motion..................................2-4
Weight.............................................................................2-4
Thrust..............................................................................2-5
Drag.................................................................................2-5
Profile Drag.................................................................2-5
Induced Drag...............................................................2-6
Parasite Drag...............................................................2-6
Total Drag...................................................................2-6
Airfoil ............................................................................2-6
Airfoil Terminology and Definitions...........................2-6
Airfoil Types...............................................................2-7
Symmetrical Airfoil.................................................2-7
Nonsymmetrical Airfoil (Cambered).......................2-7
Rotor Blade and Hub Definitions............................2-8
Airflow and Reactions in the Rotor System....................2-8
Relative Wind..............................................................2-8
Rotational Relative Wind (Tip-Path Plane)................2-8
Resultant Relative Wind..............................................2-8
Induced Flow (Downwash) ..................................2-10
Rotor Blade Angles...................................................2-10
Angle of Incidence.................................................2-10
Angle of Attack......................................................2-10
Powered Flight..............................................................2-13
Hovering Flight.............................................................2-13
Translating Tendency (Drift)....................................2-14
Pendular Action.........................................................2-14
Coriolis Effect (Law of Conservation of Angular
Momentum) ..............................................................2-15
Gyroscopic Precession..............................................2-16
Vertical Flight...............................................................2-17
Forward Flight..............................................................2-17
Airflow in Forward Flight ........................................2-17
Advancing Blade ..................................................2-18
Retreating Blade ...................................................2-18
Dissymmetry of Lift..............................................2-18
Translational Lift.......................................................2-19
Effective Translational Lift (ETL).........................2-20
Translational Thrust...............................................2-21
Induced Flow.............................................................2-21
Transverse Flow Effect.............................................2-22
Sideward Flight.............................................................2-22
Rearward Flight............................................................2-23
Turning Flight...............................................................2-23
Autorotation..................................................................2-24
Hovering Autorotation..............................................2-24
Autorotation (Forward Flight)...................................2-25
Chapter Summary.........................................................2-27
Chapter 3
Helicopter Flight Controls...................................3-1
Introduction.....................................................................3-1
Collective Pitch Control..................................................3-2
Throttle Control..............................................................3-2
Governor/Correlator . .....................................................3-2
Cyclic Pitch Control........................................................3-3
Antitorque Pedals............................................................3-4
Chapter Summary...........................................................3-5
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Chapter 4
Helicopter Components, Sections, and
Systems.................................................................4-1
Introduction.....................................................................4-1
Airframe..........................................................................4-1
Fuselage..........................................................................4-2
Main Rotor System.........................................................4-2
Semirigid Rotor System..............................................4-2
Rigid Rotor System.....................................................4-3
Fully Articulated Rotor System...................................4-4
Tandem Rotor..............................................................4-6
Swash Plate Assembly....................................................4-6
Freewheeling Unit...........................................................4-6
Antitorque System..........................................................4-7
Antitorque Drive Systems...............................................4-8
Engines............................................................................4-8
Reciprocating Engines.................................................4-8
Turbine Engines..........................................................4-8
Compressor..............................................................4-8
Combustion Chamber..............................................4-9
Turbine.....................................................................4-9
Accessory Gearbox................................................4-10
Transmission System....................................................4-10
Main Rotor Transmission..........................................4-10
Dual Tachometers..................................................4-10
Structural Design...................................................4-11
Clutch........................................................................4-11
Belt Drive Clutch...................................................4-11
Centrifugal Clutch.................................................4-12
Fuel Systems.................................................................4-12
Fuel Supply System...................................................4-12
Engine Fuel Control System.....................................4-13
Carburetor Ice...............................................................4-13
Electrical Systems.........................................................4-14
Hydraulics.....................................................................4-14
Stability Augmentations Systems.................................4-16
Force Trim.................................................................4-16
Active Augmentation Systems .................................4-16
Autopilot....................................................................4-17
Environmental Systems.............................................4-17
Anti-Icing Systems........................................................4-18
Engine Anti-Ice.........................................................4-18
Carburetor Icing........................................................4-18
Airframe Anti-Ice......................................................4-18
Deicing .....................................................................4-18
Chapter Summary.........................................................4-18
Chapter 5
Rotorcraft Flight Manual......................................5-1
Introduction.....................................................................5-1
viii
Preliminary Pages...........................................................5-2
General Information (Section 1).....................................5-2
Operating Limitations (Section 2)..................................5-2
Instrument Markings...................................................5-2
Airspeed Limitations...................................................5-2
Altitude Limitations....................................................5-3
Rotor Limitations........................................................5-3
Powerplant Limitations...............................................5-3
Flight Limitations........................................................5-4
Placards.......................................................................5-4
Emergency Procedures (Section 3).................................5-4
Normal Procedures (Section 4).......................................5-5
Performance (Section 5).................................................5-5
Weight and Balance (Section 6).....................................5-5
Aircraft and Systems Description (Section 7)................5-5
Handling, Servicing, and Maintenance (Section 8)........5-5
Supplements (Section 9).................................................5-6
Safety and Operational Tips (Section 10).......................5-6
Chapter Summary...........................................................5-6
Chapter 6
Weight and Balance.............................................6-1
Introduction.....................................................................6-1
Weight.............................................................................6-2
Basic Empty Weight....................................................6-2
Maximum Gross Weight.............................................6-2
Weight Limitations......................................................6-2
Balance........................................................................6-2
Center of Gravity.........................................................6-2
CG Forward of Forward Limit....................................6-2
CG Aft of Aft Limit....................................................6-3
Lateral Balance............................................................6-3
Weight and Balance Calculations...................................6-3
Reference Datum.........................................................6-4
Chapter Summary........................................................6-5
Chapter 7
Helicopter Performance.......................................7-1
Introduction.....................................................................7-1
Factors Affecting Performance.......................................7-2
Moisture (Humidity)...................................................7-2
Weight......................................................................7-2
Winds..........................................................................7-2
Performance Charts.........................................................7-2
Autorotational Performance........................................7-2
Hovering Performance................................................7-3
Sample Hover Problem 1.........................................7-3
Sample Hover Problem 2.........................................7-4
Sample Hover Problem 3.........................................7-4
Climb Performance.....................................................7-4
Sample Cruise or Level Flight Problem..................7-6
Sample Climb Problem............................................7-6
Chapter Summary...........................................................7-6
Chapter 8
Ground Procedures and Flight Preparations.....8-1
Introduction.....................................................................8-1
Preflight...........................................................................8-2
Minimum Equipment Lists (MELs) and Operations
with Inoperative Equipment........................................8-2
Engine Start And Rotor Engagement..............................8-3
Rotor Safety Considerations........................................8-3
Aircraft Servicing........................................................8-4
Safety In and Around Helicopters...................................8-4
Ramp Attendants and Aircraft Servicing Personnel...8-4
Passengers...................................................................8-4
Pilot at the Flight Controls..........................................8-6
After Landing and Securing........................................8-6
Chapter Summary...........................................................8-6
Chapter 9
Basic Flight Maneuvers.......................................9-1
Introduction.....................................................................9-1
The Four Fundamentals..................................................9-2
Guidelines ..................................................................9-2
Vertical Takeoff to a Hover............................................9-3
Technique....................................................................9-3
Common Errors...........................................................9-3
Hovering.........................................................................9-3
Technique....................................................................9-3
Common Errors...........................................................9-4
Hovering Turn.................................................................9-4
Technique....................................................................9-4
Common Errors...........................................................9-5
Hovering—Forward Flight.............................................9-5
Technique....................................................................9-5
Common Errors...........................................................9-6
Hovering—Sideward Flight............................................9-6
Technique....................................................................9-6
Common Errors...........................................................9-6
Hovering—Rearward Flight...........................................9-6
Technique....................................................................9-7
Common Errors...........................................................9-7
Taxiing............................................................................9-7
Hover Taxi...................................................................9-7
Air Taxi.......................................................................9-7
Technique................................................................9-7
Common Errors.......................................................9-8
Surface Taxi................................................................9-8
Technique................................................................9-8
Common Errors.......................................................9-8
Normal Takeoff From a Hover.......................................9-8
Technique....................................................................9-8
Common Errors...........................................................9-9
Normal Takeoff From the Surface..................................9-9
Technique....................................................................9-9
Common Errors...........................................................9-9
Crosswind Considerations During Takeoffs.................9-10
Straight-and-Level Flight..............................................9-10
Technique..................................................................9-10
Common Errors.........................................................9-11
Turns.............................................................................9-11
Technique..................................................................9-11
Slips...........................................................................9-12
Skids..........................................................................9-12
Normal Climb...............................................................9-13
Technique..................................................................9-13
Common Errors.........................................................9-13
Normal Descent............................................................9-13
Technique..................................................................9-13
Common Errors.........................................................9-13
Ground Reference Maneuvers......................................9-14
Rectangular Course...................................................9-14
Technique..............................................................9-14
Common Errors.....................................................9-15
S-Turns......................................................................9-15
Technique..............................................................9-15
Common Errors.....................................................9-16
Turns Around a Point................................................9-16
Technique..............................................................9-17
S-Turn Common Errors . ..........................................9-17
Traffic Patterns..............................................................9-17
Approaches...................................................................9-19
Normal Approach to a Hover....................................9-19
Technique..............................................................9-19
Common Errors.....................................................9-20
Normal Approach to the Surface...............................9-20
Technique..............................................................9-20
Common Errors.....................................................9-20
Crosswind During Approaches.................................9-20
Go-Around....................................................................9-20
Chapter Summary.........................................................9-20
Chapter 10
Advanced Flight Maneuvers..............................10-1
Introduction...................................................................10-1
Reconnaissance Procedures..........................................10-2
High Reconnaissance................................................10-2
Low Reconnaissance.................................................10-2
Ground Reconnaissance............................................10-2
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Maximum Performance Takeoff...................................10-2
Technique..................................................................10-3
Common Errors.........................................................10-3
Running/Rolling Takeoff..............................................10-3
Technique..................................................................10-4
Common Errors.........................................................10-4
Rapid Deceleration or Quick Stop ...............................10-4
Technique..................................................................10-4
Common Errors.........................................................10-5
Steep Approach.............................................................10-5
Technique..................................................................10-6
Common Errors.........................................................10-6
Shallow Approach and Running/Roll-On Landing.......10-6
Technique..................................................................10-7
Common Errors.........................................................10-7
Slope Operations...........................................................10-7
Slope Landing...........................................................10-7
Technique..............................................................10-7
Common Errors.....................................................10-8
Slope Takeoff............................................................10-8
Technique..............................................................10-9
Common Errors.....................................................10-9
Confined Area Operations.............................................10-9
Approach.................................................................10-10
Takeoff ...................................................................10-10
Common Errors.......................................................10-10
Pinnacle and Ridgeline Operations.............................10-10
Approach and Landing............................................10-11
Takeoff....................................................................10-11
Common Errors.......................................................10-12
Chapter Summary.......................................................10-12
Chapter 11
Helicopter Emergencies and Hazards..............11-1
Introduction...................................................................11-1
Autorotation..................................................................11-2
Straight-In Autorotation............................................11-3
Technique..............................................................11-3
Common Errors.....................................................11-4
Autorotation With Turns...........................................11-5
Technique..............................................................11-5
Common Errors.....................................................11-6
Practice Autorotation With a Power Recovery ........11-6
Technique..............................................................11-6
Common Errors.....................................................11-7
Power Failure in a Hover..........................................11-7
Technique..............................................................11-7
Common Errors.....................................................11-7
Height/Velocity Diagram..............................................11-8
The Effect of Weight Versus Density Altitude.........11-9
Common Errors.........................................................11-9
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Settling With Power (Vortex Ring State).....................11-9
Common Errors.......................................................11-11
Retreating Blade Stall.................................................11-11
Common Errors.......................................................11-11
Ground Resonance......................................................11-11
Dynamic Rollover.......................................................11-12
Critical Conditions..................................................11-12
Cyclic Trim.............................................................11-13
Normal Takeoffs and Landings...............................11-13
Slope Takeoffs and Landings..................................11-13
Use of Collective.....................................................11-13
Precautions..............................................................11-14
Low-G Conditions and Mast Bumping.......................11-14
Low Rotor RPM and Blade Stall................................11-15
Recovery From Low Rotor RPM................................11-15
System Malfunctions..................................................11-16
Antitorque System Failure......................................11-16
Landing—Stuck Left Pedal.....................................11-16
Landing—Stuck Neutral or Right Pedal ................11-17
Loss of Tail Rotor Effectiveness (LTE)..................11-17
Main Rotor Disk Interference (285–315°)..............11-19
Weathercock Stability (120–240°)..........................11-20
LTE at Altitude........................................................11-20
Reducing the Onset of LTE.....................................11-20
Recovery Technique................................................11-20
Main Drive Shaft or Clutch Failure.........................11-21
Hydraulic Failure.....................................................11-21
Governor or Fuel Control Failure............................11-21
Abnormal Vibration................................................11-21
Low-Frequency Vibrations..................................11-22
Medium- and High-Frequency Vibrations...........11-22
Tracking and Balance..........................................11-22
Multiengine Emergency Operations...........................11-22
Single-Engine Failure . ...........................................11-22
Dual-Engine Failure ...............................................11-22
Lost Procedures...........................................................11-22
Emergency Equipment and Survival Gear..................11-23
Chapter Summary.......................................................11-23
Chapter 12
Attitude Instrument Flying.................................12-1
Introduction...................................................................12-1
Flight Instruments.........................................................12-2
Instrument Check .....................................................12-2
Airspeed Indicator ....................................................12-2
Altimeter....................................................................12-2
Turn Indicator........................................................12-2
Magnetic Compass....................................................12-3
Helicopter Control and Performance ...........................12-3
Helicopter Control........................................................12-3
Common Errors of Attitude Instrument Flying.........12-4
Fixation......................................................................12-4
Omission....................................................................12-4
Emphasis...................................................................12-4
Inadvertent Entry into IMC.......................................12-4
Glass Cockpit or Advanced Avionics Aircraft.............12-5
Chapter Summary.........................................................12-5
Chapter 13
Night Operations................................................13-1
Introduction...................................................................13-1
Visual Deficiencies.......................................................13-2
Night Myopia............................................................13-2
Hyperopia..................................................................13-2
Astigmatism..............................................................13-2
Presbyopia.................................................................13-2
Vision in Flight.............................................................13-2
Visual Acuity.............................................................13-3
The Eye.....................................................................13-4
Cones.........................................................................13-4
Rods...........................................................................13-4
Night Vision..................................................................13-4
Night Scanning..........................................................13-4
Obstruction Detection...............................................13-6
Aircraft Lighting.......................................................13-6
Visual Illusions..........................................................13-6
Relative-Motion Illusion...........................................13-6
Confusion With Ground Lights.................................13-6
Reversible Perspective Illusion.................................13-6
Flicker Vertigo..........................................................13-7
Night Flight...................................................................13-7
Preflight.....................................................................13-7
Cockpit Lights...........................................................13-8
Engine Starting and Rotor Engagement....................13-8
Taxi Technique..........................................................13-8
Takeoff......................................................................13-8
En Route Procedures.................................................13-8
Collision Avoidance at Night....................................13-9
Approach and Landing..............................................13-9
Illusions Leading to Landing Errors..........................13-9
Featureless Terrain Illusion...................................13-9
Atmospheric Illusions............................................13-9
Ground Lighting Illusions......................................13-9
Helicopter Night VFR Operations..............................13-10
Chapter Summary.......................................................13-10
Chapter 14
Effective Aeronautical Decision-Making..........14-1
Introduction...................................................................14-1
Aeronautical Decision-Making (ADM)........................14-2
Scenario.....................................................................14-2
Trescott Tips..............................................................14-3
The Decision-Making Process..................................14-4
Defining the Problem.............................................14-4
Choosing a Course of Action.................................14-4
Implementing the Decision and Evaluating the
Outcome.................................................................14-4
Decision-Making Models..........................................14-5
Pilot Self-Assessment...................................................14-6
Curiosity: Healthy or Harmful?.................................14-6
The PAVE Checklist.................................................14-6
Single-Pilot Resource Management..............................14-7
Risk Management.........................................................14-9
Four Risk Elements...................................................14-9
Assessing Risk.........................................................14-10
Using the 3P Model To Form Good Safety Habits.14-11
Workload or Task Management..................................14-12
Situational Awareness.................................................14-13
Obstacles to Maintaining Situational Awareness . .14-14
Operational Pitfalls..................................................14-15
Controlled Flight Into Terrain (CFIT) Awareness......14-15
Automation Management............................................14-18
Chapter Summary.......................................................14-18
Glossary...............................................................G-1
Index.......................................................................I-1
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Chapter 1
Introduction to the Helicopter
Introduction
A helicopter is an aircraft that is lifted and propelled by one
or more horizontal rotors, each rotor consisting of two or
more rotor blades. Helicopters are classified as rotorcraft
or rotary-wing aircraft to distinguish them from fixed-wing
aircraft because the helicopter derives its source of lift from
the rotor blades rotating around a mast. The word “helicopter”
is adapted from the French hélicoptère, coined by Gustave de
Ponton d’Amécourt in 1861. It is linked to the Greek words
helix/helikos (“spiral” or “turning”) and pteron (“wing”).
1-1
As an aircraft, the primary advantages of the helicopter are due
to the rotor blades that revolve through the air, providing lift
without requiring the aircraft to move forward. This creates
the ability of the helicopter to take off and land vertically
without the need for runways. For this reason, helicopters are
often used in congested or isolated areas where fixed-wing
aircraft are not able to take off or land. The lift from the rotor
also allows the helicopter to hover in one area and to do so
more efficiently than other forms of vertical takeoff and
landing aircraft, allowing it to accomplish tasks that fixedwing aircraft are unable to perform. [Figures 1-1 and 1-2]
Figure 1-2. Search and rescue helicopter landing in a confined area.
main rotor, it was the single main rotor with an antitorque tail
rotor configuration design that would come to be recognized
worldwide as the helicopter.
Turbine Age
In 1951, at the urging of his contacts at the Department of
the Navy, Charles H. Kaman modified his K-225 helicopter
with a new kind of engine, the turbo-shaft engine. This
adaptation of the turbine engine provided a large amount of
horsepower to the helicopter with a lower weight penalty
than piston engines, heavy engine blocks, and auxiliary
components. On December 11, 1951, the K-225 became
the first turbine-powered helicopter in the world. Two years
later, on March 26, 1954, a modified Navy HTK‑1, another
Kaman helicopter, became the first twin-turbine helicopter
to fly. However, it was the Sud Aviation Alouette II that
would become the first helicopter to be produced with a
turbine engine.
Figure 1-1. Search and rescue helicopter conducting a pinnacle
approach.
Piloting a helicopter requires a great deal of training and skill,
as well as continuous attention to the machine. The pilot must
think in three dimensions and must use both arms and both
legs constantly to keep the helicopter in the air. Coordination,
control touch, and timing are all used simultaneously when
flying a helicopter.
Although helicopters were developed and built during the
first half-century of flight, some even reaching limited
production; it was not until 1942 that a helicopter designed by
Igor Sikorsky reached full-scale production, with 131 aircraft
built. Even though most previous designs used more than one
1-2
Reliable helicopters capable of stable hover flight were
developed decades after fixed-wing aircraft. This is largely
due to higher engine power density requirements than fixedwing aircraft. Improvements in fuels and engines during
the first half of the 20th century were a critical factor in
helicopter development. The availability of lightweight
turbo-shaft engines in the second half of the 20th century led
to the development of larger, faster, and higher-performance
helicopters. The turbine engine has the following advantages
over a reciprocating engine: less vibration, increased
aircraft performance, reliability, and ease of operation.
While smaller and less expensive helicopters still use piston
engines, turboshaft engines are the preferred powerplant for
helicopters today.
Uses
Rotor System
Due to the unique operating characteristics of the helicopter—
its ability to take off and land vertically, to hover for extended
periods of time, and the aircraft’s handling properties under
low airspeed conditions—it has been chosen to conduct tasks
that were previously not possible with other aircraft or were
too time- or work-intensive to accomplish on the ground.
Today, helicopters are used for transportation, construction,
firefighting, search and rescue, and a variety of other jobs
that require its special capabilities. [Figure 1-3]
The helicopter rotor system is the rotating part of a
helicopter that generates lift. A rotor system may be mounted
horizontally, as main rotors are, providing lift vertically; it
may be mounted vertically, such as a tail rotor, to provide
lift horizontally as thrust to counteract torque effect. In the
case of tilt rotors, the rotor is mounted on a nacelle that
rotates at the edge of the wing to transition the rotor from a
horizontal mounted position, providing lift horizontally as
thrust, to a vertical mounted position providing lift exactly
as a helicopter.
Tandem rotor (sometimes referred to as dual rotor)
helicopters have two large horizontal rotor assemblies; a twin
rotor system, instead of one main assembly and a smaller
tail rotor. [Figure 1-4] Single rotor helicopters need a tail
rotor to neutralize the twisting momentum produced by the
single large rotor. Tandem rotor helicopters, however, use
counter-rotating rotors, with each canceling out the other’s
torque. Counter-rotating rotor blades won’t collide with and
destroy each other if they flex into the other rotor’s pathway.
This configuration also has the advantage of being able to
hold more weight with shorter blades, since there are two
sets. Also, all of the power from the engines can be used for
lift, whereas a single rotor helicopter uses power to counter
the torque. Because of this, tandem helicopters are among
some of the most powerful and fastest.
Figure 1-4. Tandem rotor helicopters.
Figure 1-3. The many uses for a helicopter include search and rescue
Coaxial rotors are a pair of rotors turning in opposite
directions, but mounted on a mast, with the same axis of
rotation, one above the other. This configuration is a noted
feature of helicopters produced by the Russian Kamov
helicopter design bureau. [Figure 1-5]
(top), firefighting (middle), and construction (bottom).
1-3
Hub
Mast
Rotor blades
Figure 1-5. Coaxial rotors.
Figure 1-7. Basic components of the rotor system.
Intermeshing rotors on a helicopter are a set of two rotors
turning in opposite directions, with each rotor mast mounted
on the helicopter with a slight angle to the other so that
the blades intermesh without colliding. [Figure 1-6] The
arrangement allows the helicopter to function without the
need for a tail rotor. This configuration is sometimes referred
to as a synchropter. The arrangement was developed in
Germany for a small anti-submarine warfare helicopter, the
Flettner Fl 282 Kolibri. During the Cold War the American
Kaman Aircraft company produced the HH-43 Huskie, for
USAF firefighting purposes. Intermeshing rotored helicopters
have high stability and powerful lifting capability. The latest
Kaman K-MAX model is a dedicated sky crane design used
for construction work.
classified according to how the main rotor blades are attached
and move relative to the main rotor hub. There are three basic
classifications: semirigid, rigid, or fully articulated, although
some modern rotor systems use an engineered combination
of these types. All three rotor systems are discussed with
greater detail in Chapter 5, Helicopter Systems.
Figure 1-6. HH-43 Huskie with intermeshing rotors.
The rotor consists of a mast, hub, and rotor blades. [Figure 1-7]
The mast is a hollow cylindrical metal shaft which extends
upwards from and is driven by the transmission. At the
top of the mast is the attachment point for the rotor blades
called the hub. The rotor blades are then attached to the hub
by a number of different methods. Main rotor systems are
1-4
With a single main rotor helicopter, the creation of torque as
the engine turns the rotor creates a torque effect that causes
the body of the helicopter to turn in the opposite direction of
the rotor (Newton’s Third Law: Every action has an equal
and opposite reaction, as explained in Chapter 2, General
Aerodynamics). To eliminate this effect, some sort of
antitorque control must be used with a sufficient margin of
power available to allow the helicopter to maintain its heading
and prevent the aircraft from moving unsteadily. The three
most common controls used today are the traditional tail
rotor, Fenestron (also called a fantail), and the NOTAR®.
All three antitorque designs will be discussed in chapter 5.
Rotor Configurations
Most helicopters have a single, main rotor but require a
separate rotor to overcome torque which is a turning or
twisting force. This is accomplished through a variable
pitch, antitorque rotor or tail rotor. This is the design that
Igor Sikorsky settled on for his VS-300 helicopter shown
in Figure 1-8. It has become the recognized convention for
helicopter design, although designs do vary. When viewed
from above, designs from Germany, United Kingdom, and
the United States are said to rotate counter-clockwise, all
others are said to rotate clockwise. This can make it difficult
when discussing aerodynamic effects on the main rotor
between different designs, since the effects may manifest on
opposite sides of each aircraft. Throughout this handbook,
all examples are based on a counter-clockwise rotating main
rotor system.
at the end of the tail boom provides an angled drive for the tail
rotor and may also include gearing to adjust the output to the
optimum rotational speed typically measured in revolutions
per minute (rpm) for the tail rotor. On some larger helicopters,
intermediate gearboxes are used to angle the tail rotor drive
shaft from along the tail boom or tailcone to the top of the
tail rotor pylon, which also serves as a vertical stabilizing
airfoil to alleviate the power requirement for the tail rotor in
forward flight. The pylon (or vertical fin) may also provide
limited antitorque within certain airspeed ranges in the event
that the tail rotor or the tail rotor flight controls fail.
Controlling Flight
Figure 1-8. Igor Sikorsky designed the VS-300 helicopter
incorporating the tail rotor into the design.
Tail Rotor
The tail rotor is a smaller rotor mounted vertically or nearvertically on the tail of a traditional single-rotor helicopter.
The tail rotor either pushes or pulls against the tail to counter
the torque. The tail rotor drive system consists of a drive shaft
powered from the main transmission and a gearbox mounted
at the end of the tail boom. [Figure 1-9] The drive shaft may
consist of one long shaft or a series of shorter shafts connected
at both ends with flexible couplings. The flexible couplings
allow the drive shaft to flex with the tail boom. The gearbox
Tail rotor driveshaft
located inside
of tail body
A helicopter has four flight control inputs: cyclic, collective,
antitorque pedals, and throttle. The cyclic control is usually
located between the pilot’s legs and is commonly called the
“cyclic stick” or simply “cyclic.” On most helicopters, the
cyclic is similar to a joystick. Although, the Robinson R-22
and R-44 have a unique teetering bar cyclic control system
and a few helicopters have a cyclic control that descends into
the cockpit from overhead. The control is called the cyclic
because it can vary the pitch of the rotor blades throughout
each revolution of the main rotor system (i.e., through each
cycle of rotation) to develop unequal lift (thrust). The result
is to tilt the rotor disk in a particular direction, resulting in
the helicopter moving in that direction. If the pilot pushes
the cyclic forward, the rotor disk tilts forward, and the rotor
produces a thrust in the forward direction. If the pilot pushes
the cyclic to the side, the rotor disk tilts to that side and
produces thrust in that direction, causing the helicopter to
hover sideways. [Figure 1-10]
Tail rotor
Swash plate
Tail rotor gearbox
Pitch change links
Cross Head
Figure 1-10. Cyclic controls changing the pitch of the rotor blades.
Figure 1-9. Basic tail rotor components.
The collective pitch control, or collective, is located on the
left side of the pilot’s seat with a pilot selected variable
friction control to prevent inadvertent movement. The
1-5
collective changes the pitch angle of all the main rotor blades
collectively (i.e., all at the same time) and independently of
their position. Therefore, if a collective input is made, all
the blades change equally, increasing or decreasing total
lift or thrust, with the result of the helicopter increasing or
decreasing in altitude or airspeed.
The antitorque pedals are located in the same position as the
rudder pedals in a fixed-wing aircraft, and serve a similar
purpose, namely to control the direction in which the nose
of the aircraft is pointed. Application of the pedal in a given
direction changes the pitch of the tail rotor blades, increasing
or reducing the thrust produced by the tail rotor and causing
the nose to yaw in the direction of the applied pedal. The
pedals mechanically change the pitch of the tail rotor, altering
the amount of thrust produced.
Helicopter rotors are designed to operate at a specific rpm.
The throttle controls the power produced by the engine, which
is connected to the rotor by a transmission. The purpose of
the throttle is to maintain enough engine power to keep the
rotor rpm within allowable limits in order to keep the rotor
producing enough lift for flight. In single-engine helicopters,
the throttle control is a motorcycle-style twist grip mounted
on the collective control while dual-engine helicopters have a
power lever for each engine. [Figure 1-11] Helicopter flight
controls are discussed in greater detail throughout Chapter 4,
Helicopter Flight Controls.
Fuel control or carburetor
30
15
5
50
70
where it is required to be. Despite the complexity of the
task, the control inputs in a hover are simple. The cyclic is
used to eliminate drift in the horizontal direction that is to
control forward and back, right and left. The collective is
used to maintain altitude. The pedals are used to control nose
direction or heading. It is the interaction of these controls that
makes hovering so difficult, since an adjustment in any one
control requires an adjustment of the other two, creating a
cycle of constant correction.
Displacing the cyclic forward causes the nose to pitch down
initially, with a resultant increase in airspeed and loss of
altitude. Aft cyclic causes the nose to pitch up initially,
slowing the helicopter and causing it to climb; however, as
the helicopter reaches a state of equilibrium, the horizontal
stabilizer levels the helicopter airframe to minimize drag,
unlike an airplane. [Figure 1-12] Therefore, the helicopter
has very little pitch deflection up or down when the helicopter
is stable in a flight mode. The variation from absolutely
level depends on the particular helicopter and the horizontal
stabilizer function. Increasing collective (power) while
maintaining a constant airspeed induces a climb while
decreasing collective causes a descent. Coordinating these
two inputs, down collective plus aft cyclic or up collective
plus forward cyclic, results in airspeed changes while
maintaining a constant altitude. The pedals serve the same
function in both a helicopter and a fixed-wing aircraft, to
maintain balanced flight. This is done by applying a pedal
input in whichever direction is necessary to center the ball in
the turn and bank indicator. Flight maneuvers are discussed in
greater detail throughout Chapter 9, Basic Flight Maneuvers.
85
100
Twist grip throttle
Horizontal stabilizer
Throttle linkage
Throttle cable
Collective control
Figure 1-11. The throttle control mounted at the end of the collective
control.
Figure 1-12. The horizontal stabilizer levels the helicopter airframe
Flight Conditions
There are two basic flight conditions for a helicopter—hover
and forward flight. Hovering is the most challenging part of
flying a helicopter. This is because a helicopter generates its
own gusty air while in a hover, which acts against the fuselage
and flight control surfaces. The end result is constant control
inputs and corrections by the pilot to keep the helicopter
1-6
to minimize drag during flight.
Chapter Summary
This chapter gives the reader an overview of the history
of the helicopter, its many uses, and how it has developed
throughout the years. The chapter also introduces basic terms
and explanations of the helicopter components, sections, and
the theory behind how the helicopter flies.
1-7
1-8
Chapter 2
Aerodynamics of Flight
Introduction
This chapter presents aerodynamic fundamentals and
principles as they apply to helicopters. The content relates to
flight operations and performance of normal flight tasks. It
covers theory and application of aerodynamics for the pilot,
whether in flight training or general flight operations.
2-1
Forces Acting on the Aircraft
Once a helicopter leaves the ground, it is acted upon by
four aerodynamic forces; thrust, drag, lift and weight.
Understanding how these forces work and knowing how to
control them with the use of power and flight controls are
essential to flight. [Figure 2-1] They are defined as follows:
•
•
Thrust—the forward force produced by the power
plant/propeller or rotor. It opposes or overcomes the
force of drag. As a general rule, it acts parallel to the
longitudinal axis. However, this is not always the case,
as explained later.
Drag—a rearward, retarding force caused by
disruption of airflow by the wing, rotor, fuselage, and
other protruding objects. Drag opposes thrust and acts
rearward parallel to the relative wind.
•
Weight—the combined load of the aircraft itself, the
crew, the fuel, and the cargo or baggage. Weight pulls
the aircraft downward because of the force of gravity.
It opposes lift and acts vertically downward through
the aircraft’s center of gravity (CG).
•
Lift—opposes the downward force of weight, is
produced by the dynamic effect of the air acting on
the airfoil, and acts perpendicular to the flightpath
through the center of lift.
For a more in-depth explanation of general aerodynamics,
refer to the Pilot’s Handbook of Aeronautical Knowledge.
Lift
Drag
Thrust
a direction perpendicular to that flow, the force required to
do this work creates an equal and opposite force that is lift.
The object may be moving through a stationary fluid, or the
fluid may be flowing past a stationary object—these two are
effectively identical as, in principle, it is only the frame of
reference of the viewer which differs. The lift generated by
an airfoil depends on such factors as:
•
Speed of the airflow
•
Density of the air
•
Total area of the segment or airfoil
•
Angle of attack (AOA) between the air and the airfoil
The AOA is the angle at which the airfoil meets the oncoming
airflow (or vice versa). In the case of a helicopter, the object
is the rotor blade (airfoil) and the fluid is the air. Lift is
produced when a mass of air is deflected, and it always acts
perpendicular to the resultant relative wind. A symmetric
airfoil must have a positive AOA to generate positive lift. At
a zero AOA, no lift is generated. At a negative AOA, negative
lift is generated. A cambered or nonsymmetrical airfoil may
produce positive lift at zero, or even small negative AOA.
The basic concept of lift is simple. However, the details of how
the relative movement of air and airfoil interact to produce
the turning action that generates lift are complex. In any case
causing lift, an angled flat plate, revolving cylinder, airfoil,
etc., the flow meeting the leading edge of the object is forced to
split over and under the object. The sudden change in direction
over the object causes an area of low pressure to form behind
the leading edge on the upper surface of the object. In turn,
due to this pressure gradient and the viscosity of the fluid,
the flow over the object is accelerated down along the upper
surface of the object. At the same time, the flow forced under
the object is rapidly slowed or stagnated causing an area of
high pressure. This also causes the flow to accelerate along
the upper surface of the object. The two sections of the fluid
each leave the trailing edge of the object with a downward
component of momentum, producing lift. [Figure 2-2]
Weight
Reduced
u
air press
re
Figure 2-1. Four forces acting on a helicopter in forward flight.
Lift
Lift is generated when an object changes the direction of
flow of a fluid or when the fluid is forced to move by the
object passing through it. When the object and fluid move
relative to each other and the object turns the fluid flow in
2-2
Increased air
pressure underneath
Mass of air deflected down
Figure 2-2. Production of lift.
Upp
to de er cam
flec ber
t air he
dow lps
n
Bernoulli’s Principle
Bernoulli’s principle describes the relationship between
internal fluid pressure and fluid velocity. It is a statement
of the law of conservation of energy and helps explain why
an airfoil develops an aerodynamic force. The concept of
conservation of energy states energy cannot be created or
destroyed and the amount of energy entering a system must
also exit. A simple tube with a constricted portion near the
center of its length illustrates this principle. An example is
running water through a garden hose. The mass of flow per
unit area (cross-sectional area of tube) is the mass flow rate.
In Figure 2-3, the flow into the tube is constant, neither
accelerating nor decelerating; thus, the mass flow rate through
the tube must be the same at stations 1, 2, and 3. If the crosssectional area at any one of these stations—or any given
point—in the tube is reduced, the fluid velocity must increase
to maintain a constant mass flow rate to move the same
amount of fluid through a smaller area. Fluid speeds up in
direct proportion to the reduction in area. Venturi effect is the
term used to describe this phenomenon. Figure 2-4 illustrates
what happens to mass flow rate in the constricted tube as the
dimensions of the tube change.
Venturi Flow
While the amount of total energy within a closed system (the
tube) does not change, the form of the energy may be altered.
Pressure of flowing air may be compared to energy in that the
total pressure of flowing air always remains constant unless
energy is added or removed. Fluid flow pressure has two
components—static and dynamic pressure. Static pressure
is the pressure component measured in the flow but not
moving with the flow as pressure is measured. Static pressure
is also known as the force per unit area acting on a surface.
Dynamic pressure of flow is that component existing as a
result of movement of the air. The sum of these two pressures
is total pressure. As air flows through the constriction, static
pressure decreases as velocity increases. This increases
dynamic pressure. Figure 2-5 depicts the bottom half of the
constricted area of the tube, which resembles the top half of
an airfoil. Even with the top half of the tube removed, the air
still accelerates over the curved area because the upper air
layers restrict the flow—just as the top half of the constricted
tube did. This acceleration causes decreased static pressure
above the curved portion and creates a pressure differential
caused by the variation of static and dynamic pressures.
Station 3
WATER OUTPUT
Station 2
Station 1
WATER INPUT
Figure 2-3. Water flow through a tube.
Cross-section of cylinder
Mass of air
Same
mass of air
Velocity increased
Pressure decreased
(compared to original)
Figure 2-4. Venturi effect.
2-3
Station 3
Station 2
Station 1
Upper layers act to restrict flow
Figure 2-5. Venturi flow.
Since air is much like water, the explanation for this source
of lift may be compared to the planing effect of skis on
water. The lift that supports the water skis (and the skier) is
the force caused by the impact pressure and the deflection
of water from the lower surfaces of the skis.
Under most flying conditions, the impact pressure and the
deflection of air from the lower surface of the rotor blade
provides a comparatively small percentage of the total lift.
The majority of lift is the result of decreased pressure above
the blade, rather than the increased pressure below it.
Weight
Normally, weight is thought of as being a known, fixed value,
such as the weight of the helicopter, fuel, and occupants. To
lift the helicopter off the ground vertically, the rotor system
must generate enough lift to overcome or offset the total
weight of the helicopter and its occupants. Newton’s First
Law states: “Every object in a state of uniform motion tends
to remain in that state of motion unless an external force is
applied to it.” In this case, the object is the helicopter whether
at a hover or on the ground and the external force applied to
it is lift, which is accomplished by increasing the pitch angle
of the main rotor blades. This action forces the helicopter
into a state of motion, without it the helicopter would either
remain on the ground or at a hover.
The weight of the helicopter can also be influenced by
aerodynamic loads. When you bank a helicopter while
maintaining a constant altitude, the “G” load or load factor
2-4
increases. The load factor is the actual load on the rotor
blades at any time, divided by the normal load or gross
weight (weight of the helicopter and its contents). Any time
a helicopter flies in a constant altitude curved flightpath, the
load supported by the rotor blades is greater than the total
weight of the helicopter. The tighter the curved flightpath
is, the steeper the bank is; the more rapid the flare or pullout
from a dive is, the greater the load supported by the rotor.
Therefore, the greater the load factor must be. [Figure 2-6]
9
8
Load factor - (in Gs)
Newton’s Third Law of Motion
Additional lift is provided by the rotor blade’s lower surface
as air striking the underside is deflected downward. According
to Newton’s Third Law of Motion, “for every action there
is an equal and opposite reaction,” the air that is deflected
downward also produces an upward (lifting) reaction.
7
6
5
4
3
2
1
0
0° 10° 20° 30° 40° 50° 60° 70° 80° 90°
Bank angle (in degrees)
Figure 2-6. The load factor diagram allows a pilot to calculate
the amount of “G” loading exerted with various angles of bank.
To overcome this additional load factor, the helicopter must
be able to produce more lift. If excess engine power is not
available, the helicopter either descends or has to decelerate in
order to maintain the same altitude. The load factor and, hence,
apparent gross weight increase is relatively small in banks up
to 30°. Even so, under the right set of adverse circumstances,
such as high density altitude, turbulent air, high gross weight,
and poor pilot technique, sufficient or excess power may not
be available to maintain altitude and airspeed. Pilots must take
all of these factors into consideration throughout the entire
flight from the point of ascending to a hover to landing. Above
30° of bank, the apparent increase in gross weight soars. At
30° of bank, or pitch, the apparent increase is only 16 percent,
but at 60°, it is twice the load on the wings and rotor system.
For example, if the weight of the helicopter is 1,600 pounds,
the weight supported by the rotor disk in a 30° bank at a
constant altitude would be 1,856 pounds (1,600 + 16 percent
(or 256)). In a 60° bank, it would be 3,200 pounds; in an 80°
bank, it would be almost six times as much, or 8,000 pounds.
It is important to note that each rotor blade must support a
percentage of the gross weight. In a two bladed system, each
blade of the 1,600 pound helicopter as stated above would
have to lift 50 percent or 800 pounds. If this same helicopter
had three rotor blades, each blade would have to lift only 33
percent, or 533 pounds. One additional cause of large load
factors is rough or turbulent air. The severe vertical gusts
produced by turbulence can cause a sudden increase in AOA,
resulting in increased rotor blade loads that are resisted by the
inertia of the helicopter.
Each type of helicopter has its own limitations which are based
on the aircraft structure, size, and capabilities. Regardless
of how much weight one can carry or the engine power
that it may have, they are all susceptible to aerodynamic
overloading. Unfortunately, if the pilot attempts to push
the performance envelope the consequence can be fatal.
Aerodynamic forces effect every movement in a helicopter,
whether it is increasing the collective or a steep bank angle.
Anticipating results from a particular maneuver or adjustment
of a flight control is not good piloting technique. Instead pilots
need to truly understand the capabilities of the helicopter
under any and all circumstances and plan to never exceed
the flight envelope for any situation.
attitude along with any other unfavorable condition (i.e., high
gross weight or wind gusts) is most likely to end in disaster.
The tail rotor also produces thrust. The amount of thrust is
variable through the use of the antitorque pedals and is used
to control the helicopter’s yaw.
Drag
The force that resists the movement of a helicopter through the
air and is produced when lift is developed is called drag. Drag
must be overcome by the engine to turn the rotor. Drag always
acts parallel to the relative wind. Total drag is composed of
three types of drag: profile, induced, and parasite.
Profile Drag
Profile drag develops from the frictional resistance of the
blades passing through the air. It does not change significantly
with the airfoil’s AOA, but increases moderately when
airspeed increases. Profile drag is composed of form drag and
skin friction. Form drag results from the turbulent wake caused
by the separation of airflow from the surface of a structure.
The amount of drag is related to both the size and shape of the
structure that protrudes into the relative wind. [Figure 2-7]
Form drag
FLAT PLATE
SPHERE
Thrust
Thrust, like lift, is generated by the rotation of the main rotor
system. In a helicopter, thrust can be forward, rearward,
sideward, or vertical. The resultant lift and thrust determines
the direction of movement of the helicopter.
The solidity ratio is the ratio of the total rotor blade area,
which is the combined area of all the main rotor blades, to the
total rotor disk area. This ratio provides a means to measure
the potential for a rotor system to provide thrust and lift. The
mathematical calculations needed to calculate the solidity ratio
for each helicopter may not be of importance to most pilots
but what should be are the capabilities of the rotor system
to produce and maintain lift. Many helicopter accidents are
caused from the rotor system being overloaded. Simply put,
pilots attempt maneuvers that require more lift than the rotor
system can produce or more power than the helicopter’s
powerplant can provide. Trying to land with a nose high
SPHERE WITH
A FAIRING
SPHERE INSIDE
A HOUSING
Figure 2-7. It is easy to visualize the creation of form drag by
examining the airflow around a flat plate. Streamlining decreases
form drag by reducing the airflow separation.
Skin friction is caused by surface roughness. Even though the
surface appears smooth, it may be quite rough when viewed
under a microscope. A thin layer of air clings to the rough
surface and creates small eddies that contribute to drag.
2-5
Aver
ag e
rel
a
tive
lift
cal
Ver
ti
Total lift
Induced drag
win
d
Figure 2-8. The formation of induced drag is associated with the
downward deflection of the airstream near the rotor blade.
As the air pressure differential increases with an increase in
AOA, stronger vortices form, and induced drag increases.
Since the blade’s AOA is usually lower at higher airspeeds,
and higher at low speeds, induced drag decreases as airspeed
increases and increases as airspeed decreases. Induced drag
is the major cause of drag at lower airspeeds.
Parasite Drag
Parasite drag is present any time the helicopter is moving
through the air. This type of drag increases with airspeed.
Non-lifting components of the helicopter, such as the cabin,
rotor mast, tail, and landing gear, contribute to parasite drag.
Any loss of momentum by the airstream, due to such things
as openings for engine cooling, creates additional parasite
drag. Because of its rapid increase with increasing airspeed,
parasite drag is the major cause of drag at higher airspeeds.
Parasite drag varies with the square of the velocity; therefore,
doubling the airspeed increases the parasite drag four times.
Total Drag
Total drag for a helicopter is the sum of all three drag forces.
[Figure 2-9] As airspeed increases, parasite drag increases,
2-6
Total drag
Parasite drag
Minimum
drag or L/DMAX
Drag
Induced Drag
Induced drag is generated by the airflow circulation around
the rotor blade as it creates lift. The high pressure area beneath
the blade joins the low pressure area above the blade at the
trailing edge and at the rotor tips. This causes a spiral, or
vortex, which trails behind each blade whenever lift is being
produced. These vortices deflect the airstream downward in
the vicinity of the blade, creating an increase in downwash.
Therefore, the blade operates in an average relative wind
that is inclined downward and rearward near the blade.
Because the lift produced by the blade is perpendicular to
the relative wind, the lift is inclined aft by the same amount.
The component of lift that is acting in a rearward direction
is induced drag. [Figure 2-8]
Profile drag
Induced drag
0
25
50
75
Speed
100
125
150
Figure 2-9. The total drag curve represents the combined forces of
parasite, profile, and induced drag and is plotted against airspeed.
while induced drag decreases. Profile drag remains relatively
constant throughout the speed range with some increase at
higher airspeeds. Combining all drag forces results in a total
drag curve. The low point on the total drag curve shows the
airspeed at which drag is minimized. This is the point where
the lift-to-drag ratio is greatest and is referred to as L/DMAX.
At this speed, the total lift capacity of the helicopter, when
compared to the total drag of the helicopter, is most favorable.
This is an important factor in helicopter performance.
Airfoil
Helicopters are able to fly due to aerodynamic forces
produced when air passes around the airfoil. An airfoil is
any surface producing more lift than drag when passing
through the air at a suitable angle. Airfoils are most often
associated with production of lift. Airfoils are also used for
stability (fin), control (elevator), and thrust or propulsion
(propeller or rotor). Certain airfoils, such as rotor blades,
combine some of these functions. The main and tail rotor
blades of the helicopter are airfoils, and air is forced to pass
around the blades by mechanically powered rotation. In
some conditions, parts of the fuselage, such as the vertical
and horizontal stabilizers, can become airfoils. Airfoils are
carefully structured to accommodate a specific set of flight
characteristics.
Airfoil Terminology and Definitions
•
Blade span—the length of the rotor blade from center
of rotation to tip of the blade.
•
Chord line—a straight line intersecting leading and
trailing edges of the airfoil. [Figure 2-10]
•
Chord—the length of the chord line from leading edge
to trailing edge; it is the characteristic longitudinal
dimension of the airfoil section.
•
Mean camber line—a line drawn halfway between the
upper and lower surfaces of the airfoil. [Figure 2-10]
Mean camber line
Trailing edge
Camber of upper surface
•
Angle of attack (AOA)—the angle measured between
the resultant relative wind and chord line.
•
Angle of incidence (AOI)—the angle between the
chord line of a blade and rotor hub. It is usually
referred to as blade pitch angle. For fixed airfoils,
such as vertical fins or elevators, angle of incidence
is the angle between the chord line of the airfoil and
a selected reference plane of the helicopter.
•
Center of pressure—the point along the chord line of
an airfoil through which all aerodynamic forces are
considered to act. Since pressures vary on the surface
of an airfoil, an average location of pressure variation
is needed. As the AOA changes, these pressures change
and center of pressure moves along the chord line.
Camber of lower surface
Leading edge
Chord line
Figure 2-10. Aerodynamic terms of an airfoil.
The chord line connects the ends of the mean camber
line. Camber refers to curvature of the airfoil and may
be considered curvature of the mean camber line. The
shape of the mean camber is important for determining
aerodynamic characteristics of an airfoil section.
Maximum camber (displacement of the mean camber
line from the chord line) and its location help to define
the shape of the mean camber line. The location of
maximum camber and its displacement from the chord
line are expressed as fractions or percentages of the
basic chord length. By varying the point of maximum
camber, the manufacturer can tailor an airfoil for a
specific purpose. The profile thickness and thickness
distribution are important properties of an airfoil
section.
•
Leading edge—the front edge of an airfoil.
[Figure 2-10]
•
Flightpath velocity—the speed and direction of
the airfoil passing through the air. For airfoils on
an airplane, the flightpath velocity is equal to true
airspeed (TAS). For helicopter rotor blades, flightpath
velocity is equal to rotational velocity, plus or minus
a component of directional airspeed. The rotational
velocity of the rotor blade is lowest closer to the hub
and increases outward towards the tip of the blade
during rotation.
•
Relative wind—defined as the airflow relative to
an airfoil and is created by movement of an airfoil
through the air. This is rotational relative wind for
rotary-wing aircraft and is covered in detail later. As
an induced airflow may modify flightpath velocity,
relative wind experienced by the airfoil may not be
exactly opposite its direction of travel.
•
Trailing edge—the rearmost edge of an airfoil.
•
Induced flow—the downward flow of air through the
rotor disk.
•
Resultant relative wind—relative wind modified by
induced flow.
Airfoil Types
Symmetrical Airfoil
The symmetrical airfoil is distinguished by having identical
upper and lower surfaces. [Figure 2-11] The mean camber
line and chord line are the same on a symmetrical airfoil,
and it produces no lift at zero AOA. Most light helicopters
incorporate symmetrical airfoils in the main rotor blades.
Nonsymmetrical
Symmetrical
Figure 2-11. The upper and lower curvatures are the same on a
symmetrical airfoil and vary on a nonsymmetrical airfoil.
Nonsymmetrical Airfoil (Cambered)
The nonsymmetrical airfoil has different upper and lower
surfaces, with a greater curvature of the airfoil above the
chord line than below. [Figure 2-11] The mean camber
line and chord line are different. The nonsymmetrical
airfoil design can produce useful lift at zero AOA. A
nonsymmetrical design has advantages and disadvantages.
The advantages are more lift production at a given AOA
than a symmetrical design, an improved lift-to-drag ratio,
and better stall characteristics. The disadvantages are center
of pressure travel of up to 20 percent of the chord line
(creating undesirable torque on the airfoil structure) and
greater production costs.
2-7
Blade Twist
Because of lift differential due to differing rotational relative
wind values along the blade, the blade should be designed
with a twist to alleviate internal blade stress and distribute
the lifting force more evenly along the blade. Blade twist
provides higher pitch angles at the root where velocity is
low and lower pitch angles nearer the tip where velocity
is higher. This increases the induced air velocity and blade
loading near the inboard section of the blade. [Figure 2-12]
There are two parts to wind passing a rotor blade:
Hub—on the mast is the center point and attaching
point for the root of the blade
•
Tip—the farthest outboard section of the rotor blade
•
Root—the inner end of the blade and is the point that
attaches to the hub
•
Twist—the change in blade incidence from the root
to the outer blade
Horizontal part—caused by the blades turning
plus movement of the helicopter through the air
[Figure 2-14]
•
Vertical part—caused by the air being forced down
through the rotor blades plus any movement of the air
relative to the blades caused by the helicopter climbing
or descending [Figures 2-15 and 2-16]
Rotational Relative Wind (Tip-Path Plane)
The rotation of rotor blades as they turn about the mast
produces rotational relative wind (tip-path plane). The term
rotational refers to the method of producing relative wind.
Rotational relative wind flows opposite the physical flightpath
of the airfoil, striking the blade at 90° to the leading edge and
parallel to the plane of rotation; and it is constantly changing
in direction during rotation. Rotational relative wind velocity
is highest at blade tips, decreasing uniformly to zero at the
axis of rotation (center of the mast). [Figure 2-17]
Rotor Blade and Hub Definitions
•
•
Resultant Relative Wind
The resultant relative wind at a hover is rotational relative
wind modified by induced flow. This is inclined downward
at some angle and opposite the effective flightpath of the
airfoil, rather than the physical flightpath (rotational relative
wind). The resultant relative wind also serves as the reference
plane for development of lift, drag, and total aerodynamic
force (TAF) vectors on the airfoil. [Figure 2-18] When the
helicopter has horizontal motion, airspeed further modifies
the resultant relative wind. The airspeed component of
relative wind results from the helicopter moving through
the air. This airspeed component is added to, or subtracted
from, the rotational relative wind depending on whether
the blade is advancing or retreating in relation to helicopter
movement. Introduction of airspeed relative wind also
The angular position of the main rotor blades is measured
from the helicopter’s longitudinal axis, which is usually the
nose position and the blade. The radial position of a segment
of the blade is the distance from the hub as a fraction of the
total distance.
Airflow and Reactions in the Rotor
System
Relative Wind
Knowledge of relative wind is essential for an understanding
of aerodynamics and its practical flight application for the
pilot. Relative wind is airflow relative to an airfoil. Movement
of an airfoil through the air creates relative wind. Relative
wind moves in a parallel but opposite direction to movement
of the airfoil. [Figure 2-13]
A
B
C
Tip
Root
Trim tab
A
Section near root
B
Section in center
Note: “More nose-down” tilt to blade section closer to tip
Figure 2-12. Blade twist.
2-8
C
Section near tip
Results in
n
irectio
d
Airfoil
Airfoil
Relative wind
Results in
Airfoil direction
e wind
Relativ
Relativ
directi
e wind
Results in
on
Figure 2-13. Relative wind.
Airspeed knots
290
387
183
96
Figure 2-14. Horizontal component of relative wind.
Axis of rotation
Figure 2-16. Normal induced flow velocities along the blade span
during hovering flight. Downward velocity is highest at the blade
tip where blade speed is highest. As blade speed decreases nearer
the center of the disk, downward velocity is less.
Figure 2-15. Induced flow.
2-9
Angle of incidence
Center of pressure
Rotational relative wind
Flightpath of airfoil
Chord line
Figure 2-17. Rotational relative wind.
Resultant relative wind
Angle of attack
Center of pressure
Rotational relative wind
Induced flow
Chord line
Figure 2-18. Resultant relative wind.
modifies induced flow. Generally, the downward velocity
of induced flow is reduced. The pattern of air circulation
through the disk changes when the aircraft has horizontal
motion. As the helicopter gains airspeed, the addition of
forward velocity results in decreased induced flow velocity.
This change results in an improved efficiency (additional lift)
being produced from a given blade pitch setting.
Induced Flow (Downwash)
At flat pitch, air leaves the trailing edge of the rotor blade in
the same direction it moved across the leading edge; no lift
or induced flow is being produced. As blade pitch angle is
increased, the rotor system induces a downward flow of air
through the rotor blades creating a downward component of
air that is added to the rotational relative wind. Because the
blades are moving horizontally, some of the air is displaced
downward. The blades travel along the same path and pass a
given point in rapid succession. Rotor blade action changes
the still air to a column of descending air. Therefore, each
blade has a decreased AOA due to the downwash. This
downward flow of air is called induced flow (downwash).
It is most pronounced at a hover under no-wind conditions.
[Figure 2-19]
In Ground Effect (IGE)
Ground effect is the increased efficiency of the rotor system
caused by interference of the airflow when near the ground.
The air pressure or density is increased, which acts to
decrease the downward velocity of air. Ground effect permits
relative wind to be more horizontal, lift vector to be more
2-10
vertical, and induced drag to be reduced. These conditions
allow the rotor system to be more efficient. Maximum
ground effect is achieved when hovering over smooth hard
surfaces. When hovering over surfaces as tall grass, trees,
bushes, rough terrain, and water, maximum ground effect
is reduced. Rotor efficiency is increased by ground effect
to a height of about one rotor diameter (measured from the
ground to the rotor disk) for most helicopters. Since the
induced flow velocities are decreased, the AOA is increased,
which requires a reduced blade pitch angle and a reduction
in induced drag. This reduces the power required to hover
IGE. [Figure 2-20]
Out of Ground Effect (OGE)
The benefit of placing the helicopter near the ground is lost
above IGE altitude. Above this altitude, the power required
to hover remains nearly constant, given similar conditions
(such as wind). Induced flow velocity is increased, resulting
in a decrease in AOA and a decrease in lift. Under the
correct circumstances, this downward flow can become so
localized that the helicopter and locally disturbed air will sink
at alarming rates. This effect is called settling with power
and is discussed at length in a later chapter. A higher blade
pitch angle is required to maintain the same AOA as in IGE
hover. The increased pitch angle also creates more drag. This
increased pitch angle and drag requires more power to hover
OGE than IGE. [Figure 2-21]
Rotor Blade Angles
There are two angles that enable a rotor system to produce
the lift required for a helicopter to fly: angle of incidence
and angle of attack.
Angle of Incidence
Angle of incidence is the angle between the chord line of a
main or tail rotor blade and the rotor hub. It is a mechanical
angle rather than an aerodynamic angle and is sometimes
referred to as blade pitch angle. [Figure 2-22] In the absence
of induced flow, AOA and angle of incidence are the same.
Whenever induced flow, up flow (inflow), or airspeed
modifies the relative wind, the AOA is different from the
angle of incidence. Collective input and cyclic feathering
change the angle of incidence. A change in the angle of
incidence changes the AOA, which changes the coefficient
of lift, thereby changing the lift produced by the airfoil.
Angle of Attack
AOA is the angle between the airfoil chord line and resultant
relative wind. [Figure 2-23] AOA is an aerodynamic angle
and not easy to measure. It can change with no change in
the blade pitch angle (angle of incidence, discussed earlier).
Angle of attack
Angle of attack
Less induced flow
Greater induced flow
B
Resultant relative wind
Rotational relative wind
A
Resultant relative wind
Rotational relative wind
Downward velocity of air molecules used by aft section of rotor
More horizontal
flow of air
10–20 knots
A
B
Figure 2-19. A helicopter in forward flight, or hovering with a headwind or crosswind, has more molecules of air entering the aft portion
of the rotor blade. Therefore, the angle of attack is less and the induced flow is greater at the rear of the rotor disk.
Reduced rotor-tip vortex
Altitude at one rotor diameter or less
Axis of rotation
Reduced induced drag angle
Angle of attack
Lift
Red
uced
Resultant relative wind
Reduced induced flow velocity
blad
TA
F
e pit
ch a
ngle
Rotational relative wind
Drag
Lift vector more vertical
Figure 2-20. In ground effect (IGE).
2-11
Large rotor-tip vortex
Altitude greater than one rotor diameter
Lift is perpendicular to resultant relative wind
Axis of rotation
Larger induced drag angle
Angle of attack
h bl
Resultant relative wind
Larger induced flow velocity
Lift
Hig
ade
pitc
TA
h an
gle
F
Rotational relative wind
Lift vector inclined to rear
Dra
g
Figure 2-21. Out of ground effect (OGE).
Angle of incidence
Center of pressure
Tip-path plane
Chord line
Figure 2-22. Angle of incidence.
Relative Wind
Angle of Attack
Pitch An
gle
Reference Plane
Axis of Rotation
Chord Line
Figure 2-23. The AOA is the angle between the airfoil chord line
and resultant relative wind.
When the AOA is increased, air flowing over the airfoil is
diverted over a greater distance, resulting in an increase of
air velocity and more lift. As the AOA is increased further,
2-12
it becomes more difficult for air to flow smoothly across the
top of the airfoil. At this point, the airflow begins to separate
from the airfoil and enters a burbling or turbulent pattern.
The turbulence results in a large increase in drag and loss of
lift in the area where it is taking place. Increasing the AOA
increases lift until the critical angle of attack is reached. Any
increase in the AOA beyond this point produces a stall and
a rapid decrease in lift.
Several factors may change the rotor blade AOA. The pilot
has little direct control over AOA except indirectly through
the flight control input. Collective and cyclic feathering help
to make these changes. Feathering is the rotation of the blade
about its spanwise axis by collective/cyclic inputs causing
changes in blade pitch angle. Collective feathering changes
angle of incidence equally and in the same direction on all
rotor blades simultaneously. This action changes AOA,
which changes coefficient of lift (CL), and affects overall
lift of the rotor system.
Cyclic feathering changes angle of incidence differentially
around the rotor system. Cyclic feathering creates a
differential lift in the rotor system by changing the AOA
differentially across the rotor system. Aviators use cyclic
feathering to control attitude of the rotor system. It is the
means to control rearward tilt of the rotor (blowback) caused
by flapping action and (along with blade flapping) counteract
dissymmetry of lift (discussed in chapter 3). Cyclic feathering
causes attitude of the rotor disk to change but does not change
the amount of lift the rotor system is producing.
Powered Flight
In powered flight (hovering, vertical, forward, sideward,
or rearward), the total lift and thrust forces of a rotor are
perpendicular to the tip-path plane or plane of rotation of
the rotor.
Hovering Flight
Hovering is the most challenging part of flying a helicopter.
This is because a helicopter generates its own gusty air
while in a hover, which acts against the fuselage and flight
control surfaces. The end result is constant control inputs
and corrections by the pilot to keep the helicopter where
it is required to be. Despite the complexity of the task, the
control inputs in a hover are simple. The cyclic is used to
eliminate drift in the horizontal plane, controlling forward,
backward, right and left movement or travel. The throttle, if
not governor controlled, is used to control revolutions per
minute (rpm). The collective is used to maintain altitude. The
pedals are used to control nose direction or heading. It is the
interaction of these controls that makes hovering difficult,
since an adjustment in any one control requires an adjustment
of the other two, creating a cycle of constant correction.
During hovering flight, a helicopter maintains a constant
position over a selected point, usually a few feet above the
ground. The ability of the helicopter to hover comes from the
both the lift component, which is the force developed by the
main rotor(s) to overcome gravity and aircraft weight, and
Drag
Thrust
Weight
Pilots adjust AOA through normal control manipulation of
the pitch angle of the blades. If the pitch angle is increased,
the AOA increases; if the pitch angle is reduced, the AOA
is reduced.
Lift
Most of the changes in AOA come from change in airspeed
and rate of climb or descent; others such as flapping occur
automatically due to rotor system design. Flapping is the
up and down movement of rotor blades about a hinge on a
fully articulated rotor system. The semi-rigid system does
not have a hinge but flap as a unit. The rigid rotor system
has no vertical or horizontal hinges so the blades cannot flap
or drag, but they can flex. By flexing, the blades themselves
compensate for the forces which previously required rugged
hinges. It occurs in response to changes in lift due to changing
velocity or cyclic feathering. No flapping occurs when the tippath plane is perpendicular to the mast. The flapping action
alone, or along with cyclic feathering, controls dissymmetry
of lift. Flapping is the primary means of compensating for
dissymmetry of lift.
the thrust component, which acts horizontally to accelerate or
decelerate the helicopter in the desired direction. Pilots direct
the thrust of the rotor system by using the cyclic to change the
tip-path plane as compared to the visible horizon to induce
travel or compensate for the wind and hold a position. At a
hover in a no-wind condition, all opposing forces (lift, thrust,
drag, and weight) are in balance; they are equal and opposite.
Therefore, lift and weight are equal, resulting in the helicopter
remaining at a stationary hover. [Figure 2-24]
Figure 2-24. To maintain a hover at a constant altitude, the lift
must equal the weight of the helicopter. Thrust must equal any
wind and tail rotor thrust to maintain position. The power must be
sufficient to turn the rotors and overcome the various drags and
frictions involved.
While hovering, the amount of main rotor thrust can be
changed to maintain the desired hovering altitude. This is
done by changing the angle of incidence (by moving the
collective) of the rotor blades and hence the angle of attack
(AOA) of the main rotor blades. Changing the AOA changes
the drag on the rotor blades, and the power delivered by the
engine must change as well to keep the rotor speed constant.
The weight that must be supported is the total weight of the
helicopter and its occupants. If the amount of lift is greater
than the actual weight, the helicopter accelerates upwards
until the lift force equals the weight gain altitude; if thrust is
less than weight, the helicopter accelerates downward. When
operating near the ground, the effects of the proximity to the
surface change this response.
The drag of a hovering helicopter is mainly induced drag
incurred while the blades are producing lift. There is, however,
some profile drag on the blades as they rotate through the air
and a small amount of parasite drag from the non-lift-producing
surfaces of the helicopter, such as the rotor hub, cowlings, and
2-13
landing gear. Throughout the rest of this discussion, the term
“drag” includes induced, profile and parasite drag.
An important consequence of producing thrust is torque.
As discussed in Chapter 2, Newton’s Third Law, for every
action there is an equal and opposite reaction. Therefore, as
the engine turns the main rotor system in a counterclockwise
direction, the helicopter fuselage wants to turn clockwise. The
amount of torque is directly related to the amount of engine
power being used to turn the main rotor system. Remember,
as power changes, torque changes.
To counteract this torque-induced turning tendency, an
antitorque rotor or tail rotor is incorporated into most
helicopter designs. A pilot can vary the amount of thrust
produced by the tail rotor in relation to the amount of torque
produced by the engine. As the engine supplies more power
to the main rotor, the tail rotor must produce more thrust to
overcome the increased torque effect. This control change is
accomplished through the use of antitorque pedals.
Translating Tendency (Drift)
During hovering flight, a single main rotor helicopter tends
to move in the direction of tail rotor thrust. This lateral
(or sideward) movement is called translating tendency.
[Figure 2-25]
d
Bla
ation
e rot
e
qu
To
r
e
qu
Drift
To
r
tion
Blade rota
Tail rotor
downwash
Tail rotor thrust
Figure 2-25. A tail rotor is designed to produce thrust in a direction
opposite torque. The thrust produced by the tail rotor is sufficient
to move the helicopter laterally.
To counteract this tendency, one or more of the following
features may be used. All examples are for a counterclockwise
rotating main rotor system.
•
2-14
The main transmission is mounted at a slight angle to
the left (when viewed from behind) so that the rotor
mast has a built-in tilt to oppose the tail rotor thrust.
•
Flight controls can be rigged so that the rotor disk is
tilted to the left slightly when the cyclic is centered.
Whichever method is used, the tip-path plane is tilted
slightly to the left in the hover.
•
If the transmission is mounted so the rotor shaft is
vertical with respect to the fuselage, the helicopter
“hangs” left skid low in the hover. The opposite is
true for rotor systems turning clockwise when viewed
from above. The helicopter fuselage will also be
tilted when the tail rotor is below the main rotor disk
and supplying antitorque thrust. The fuselage tilt is
caused by the imperfect balance of the tail rotor thrust
against the main rotor torque in the same plane. The
helicopter tilts due to two separate forces, the main
rotor disk tilt to neutralize the translating tendency
and the lower tail rotor thrust below the plane of the
torque action.
•
In forward flight, the tail rotor continues to push to
the right, and the helicopter makes a small angle with
the wind when the rotors are level and the slip ball
is in the middle. This is called inherent sideslip. For
some larger helicopters, the vertical fin or stabilizer
is often designed with the tail rotor mounted on them
to correct this side slip and to eliminate some of the
tilting at a hover. Also, by mounting the tail rotor
on top of the vertical fin or pylon, the antitorque is
more in line with or closer to the horizontal plane
of torque, resulting in less airframe (or body) lean
from the tail rotor. Having the tail rotor higher off the
ground reduces the risk of objects coming in contact
with the blades, but at the cost of increased weight
and complexity.
Pendular Action
Since the fuselage of the helicopter, with a single main rotor,
is suspended from a single point and has considerable mass, it
is free to oscillate either longitudinally or laterally in the same
way as a pendulum. This pendular action can be exaggerated
by overcontrolling; therefore, control movements should be
smooth and not exaggerated. [Figure 2-26]
The horizontal stabilizer tends to level the airframe in forward
flight. However, in rearward flight, the horizontal stabilizer
can press the tail downward, resulting in a tail strike if
the helicopter is moved into the wind. Normally, with the
helicopter mostly into the wind, the horizontal stabilizer
experiences less headwind component as the helicopter
begins rearward travel (downwind). When rearward flight
groundspeed equals the windspeed, then the helicopter is
merely hovering in a no-wind condition. However, rearward
hovering into the wind requires considerable care and caution
to prevent tail strikes.
Before takeoff
Lift
Resultant
blade
angle
Centrifugal
force
During takeoff
Calm wind hover
Initial rearward flight
Initial forward flight
Figure 2-26. Because the helicopter’s body has mass and is
suspended from a single point (the rotor mast head), it tends to act
much like a pendulum.
Coning
In order for a helicopter to generate lift, the rotor blades
must be turning. Rotor system rotation drives the blades into
the air, creating a relative wind component without having
to move the airframe through the air as with an airplane or
glider. Depending on the motion of the blades and helicopter
airframe, many factors cause the relative wind direction to
vary. The rotation of the rotor system creates centrifugal force
(inertia), which tends to pull the blades straight outward from
the main rotor hub. The faster the rotation is, the greater the
centrifugal force; and the slower the rotation is, the smaller
the centrifugal force. This force gives the rotor blades their
rigidity and, in turn, the strength to support the weight of
the helicopter. The maximum centrifugal force generated
is determined by the maximum operating rotor revolutions
per minute (rpm).
As lift on the blades is increased (in a takeoff, for example),
two major forces are acting at the same time—centrifugal
force acting outward, and lift acting upward. The result of
these two forces is that the blades assume a conical path
instead of remaining in the plane perpendicular to the mast.
This can be seen in any helicopter when it takes off; the rotor
disk changes from flat to a slight cone shape. [Figure 2-27]
If the rotor rpm is allowed to go too low (below the
minimum power-on rotor rpm, for example), the centrifugal
force becomes smaller and the coning angle becomes much
larger. In other words, should the rpm decrease too much,
at some point the rotor blades fold up with no chance
of recovery.
Figure 2-27. During takeoff, the combination of centrifugal force
and lift cause the rotor disk to cone upward.
Coriolis Effect (Law of Conservation of Angular
Momentum)
The Coriolis Effect is also referred to as the law of
conservation of angular momentum. It states that the value
of angular momentum of a rotating body does not change
unless an external force is applied. In other words, a rotating
body continues to rotate with the same rotational velocity
until some external force is applied to change the speed of
rotation. Angular momentum is the moment of inertia (mass
times distance from the center of rotation squared) multiplied
by the speed of rotation.
Changes in angular velocity, known as angular acceleration
and deceleration, take place as the mass of a rotating body
is moved closer to or farther away from the axis of rotation.
The speed of the rotating mass varies proportionately with
the square of the radius.
An excellent example of this principle in action is a figure
skater performing a spin on ice skates. The skater begins
rotation on one foot, with the other leg and both arms
extended. The rotation of the skater’s body is relatively
slow. When a skater draws both arms and one leg inward,
the moment of inertia (mass times radius squared) becomes
much smaller and the body is rotating almost faster than the
eye can follow. Because the angular momentum must, by
law of nature, remain the same (no external force applied),
the angular velocity must increase.
The rotor blade rotating about the rotor hub possesses angular
momentum. As the rotor begins to cone due to G-loading
maneuvers, the diameter or the rotor disk shrinks. Due to
conservation of angular momentum, the blades continue
to travel the same speed even though the blade tips have a
shorter distance to travel due to reduced disk diameter. The
action results in an increase in rotor rpm which causes a slight
increase in lift. Most pilots arrest this increase of rpm with
an increase in collective pitch. This increase in blade rpm
lift is somewhat negated by the slightly smaller disk area as
the blades cone upward.
2-15
Gyroscopic Precession
The spinning main rotor of a helicopter acts like a gyroscope.
As such, it has the properties of gyroscopic action, one of
which is precession. Gyroscopic precession is the resultant
action or deflection of a spinning object when a force is
applied to this object. This action occurs approximately 90°
in the direction of rotation from the point where the force
is applied (or 90° later in the rotation cycle). [Figure 2-28]
Examine a two-bladed rotor system to see how gyroscopic
precession affects the movement of the tip-path plane.
Moving the cyclic pitch control increases the angle of
incidence of one rotor blade with the result of a greater lifting
force being applied at that point in the plane of rotation.
This same control movement simultaneously decreases the
angle of incidence of the other blade the same amount, thus
decreasing the lifting force applied at that point in the plane of
rotation. The blade with the increased angle of incidence tends
to flap up; the blade with the decreased angle of incidence
tends to flap down. Because the rotor disk acts like a gyro, the
blades reach maximum deflection at a point approximately
90° later in the plane of rotation. Figure 2-29 illustrates the
result of a forward cyclic input. The retreating blade angle
Downward movement
response here
Upward
force
applied
here
C
Forward
B
A
Downward
force
applied
here
D
Upward movement
Figure 2-28. Gyroscopic precession.
of incidence is increased and the advancing blade angle of
incidence is decreased resulting in a tipping forward of the
tip-path plane, since maximum deflection takes place 90°
later when the blades are at the rear and front, respectively.
Angle of attack decreased
Maximum upward deflection
Blade rotation
Maximum downward deflection
ct
re
Di
ion
of
l
tr
e
av
Blade rotation
Angle of attack increased
Figure 2-29. As each blade passes the 90° position on the left in a counterclockwise main rotor blade rotation, the maximum increase
in angle of incidence occurs. As each blade passes the 90° position to the right, the maximum decrease in angle of incidence occurs.
Maximum deflection takes place 90° later—maximum upward deflection at the rear and maximum downward deflection at the front—and
the tip-path plane tips forward.
2-16
Resultant
Lift
In a rotor system using three or more blades, the movement
of the cyclic pitch control changes the angle of incidence of
each blade an appropriate amount so that the end result is
the same.
Vertical Flight
Thrust
Drag
Helicopter movement
Weight
Hovering is actually an element of vertical flight. Increasing
the angle of incidence of the rotor blades (pitch) while
keeping their rotation speed constant generates additional
lift and the helicopter ascends. Decreasing the pitch causes
the helicopter to descend. In a no-wind condition in which
lift and thrust are less than weight and drag, the helicopter
descends vertically. If lift and thrust are greater than weight
and drag, the helicopter ascends vertically. [Figure 2-30]
Resultant
Lift/thrustt
Vertical/ascent
Weig
Weight/drag
Figure 2-30. Balanced forces: hovering in a no-wind condition.
Forward Flight
In steady forward flight, with no change in airspeed or vertical
speed, the four forces of lift, thrust, drag, and weight must
be in balance. Once the tip-path plane is tilted forward, the
total lift-thrust force is also tilted forward. This resultant
lift-thrust force can be resolved into two components—lift
acting vertically upward and thrust acting horizontally in the
direction of flight. In addition to lift and thrust, there is weight
(the downward acting force) and drag (the force opposing the
motion of an airfoil through the air). [Figure 2-31]
In straight-and-level, unaccelerated forward flight (straightand-level flight is flight with a constant heading and at a
constant altitude), lift equals weight and thrust equals drag.
If lift exceeds weight, the helicopter accelerates vertically
until the forces are in balance; if thrust is less than drag,
the helicopter slows down until the forces are in balance.
As the helicopter moves forward, it begins to lose altitude
Figure 2-31. To transition to forward flight, more lift and thrust must
be generated to overcome the forces of weight and drag.
because lift is lost as thrust is diverted forward. However,
as the helicopter begins to accelerate from a hover, the rotor
system becomes more efficient due to translational lift (see
translational lift on page 2-19). The result is excess power
over that which is required to hover. Continued acceleration
causes an even larger increase in airflow, to a point, through
the rotor disk and more excess power. In order to maintain
unaccelerated flight, the pilot must understand that with
any changes in power or in cyclic movement, the helicopter
begins either to climb or to descend. Once straight-and-level
flight is obtained, the pilot should make note of the power
(torque setting) required and not make major adjustments to
the flight controls. [Figure 2-32]
Airflow in Forward Flight
Airflow across the rotor system in forward flight varies from
airflow at a hover. In forward flight, air flows opposite the
aircraft’s flightpath. The velocity of this air flow equals the
helicopter’s forward speed. Because the rotor blades turn
in a circular pattern, the velocity of airflow across a blade
depends on the position of the blade in the plane of rotation
at a given instant, its rotational velocity, and airspeed of the
helicopter. Therefore, the airflow meeting each blade varies
continuously as the blade rotates. The highest velocity of
airflow occurs over the right side (3 o’clock position) of
the helicopter (advancing blade in a rotor system that turns
counterclockwise) and decreases to rotational velocity over
the nose. It continues to decrease until the lowest velocity of
airflow occurs over the left side (9 o’clock position) of the
helicopter (retreating blade). As the blade continues to rotate,
velocity of the airflow then increases to rotational velocity
over the tail. It continues to increase until the blade is back
at the 3 o’clock position.
2-17
800
Airspeed = 120 Knots
Relative wind as a
result of aircraft
movement at 120 knots
B
er
40
60
80
100
knots
A
= 480
120
Indicated airspeed (KIAS)
Figure 2-32. Power versus airspeed chart.
The advancing blade in Figure 2-33, position A, moves in
the same direction as the helicopter. The velocity of the air
meeting this blade equals rotational velocity of the blade
plus wind velocity resulting from forward airspeed. The
retreating blade (position C) moves in a flow of air moving
in the opposite direction of the helicopter. The velocity of
airflow meeting this blade equals rotational velocity of the
blade minus wind velocity resulting from forward airspeed.
The blades (positions B and D) over the nose and tail move
essentially at right angles to the airflow created by forward
airspeed; the velocity of airflow meeting these blades equals
the rotational velocity. This results in a change to velocity
of airflow all across the rotor disk and a change to the lift
pattern of the rotor system.
Advancing Blade
As the relative wind speed of the advancing blade increases,
the blade gains lift and begins to flap up. It reaches its
maximum upflap velocity at the 3 o’clock position, where the
wind velocity is the greatest. This upflap creates a downward
flow of air and has the same effect as increasing the induced
flow velocity by imposing a downward vertical velocity
vector to the relative wind which decreases the AOA.
Retreating Blade
As relative wind speed of the retreating blade decreases,
the blade loses lift and begins to flap down. It reaches its
maximum downflap velocity at the 9 o’clock position, where
wind velocity is the least. This downflap creates an upward
flow of air and has the same effect as decreasing the induced
2-18
C
ity
loc
ve
l
na
0
Maximum
continuous
level
(horizontal)
flight
airspeed (VH)
D
Ro
ta
tio
0
Minimum power
for level flight (VY)
Increasing power for
decreasing airspeed
tation
200
D
B
f ro
no
tio
w
Po
400
Relative wind as a
result of aircraft
movement at 120 knots
c
ire
re
qu
ire
dt
oh
ove
A
C
rO
Increasing power for
decreasing airspeed
600
Power required (horsepower)
GE
Maximum continuous power available
–
480
Knots
= Rotational
Velocity
120
Knots
=
Aircraft
Airspeed
360
Knots
=
Wind
Velocity
+
480
Knots
= Rotational
Velocity
120
Knots
=
Aircraft
Airspeed
600
Knots
=
Wind
Velocity
Figure 2-33. Airflow in forward flight.
flow velocity by imposing an upward velocity vertical vector
to the relative wind which increases the AOA.
Dissymmetry of Lift
Dissymmetry of lift is the differential (unequal) lift between
advancing and retreating halves of the rotor disk caused by the
different wind flow velocity across each half. This difference
in lift would cause the helicopter to be uncontrollable in any
situation other than hovering in a calm wind. There must
be a means of compensating, correcting, or eliminating this
unequal lift to attain symmetry of lift.
When the helicopter moves through the air, the relative
airflow through the main rotor disk is different on the
advancing side than on the retreating side. The relative wind
encountered by the advancing blade is increased by the
forward speed of the helicopter, while the relative wind speed
acting on the retreating blade is reduced by the helicopter’s
forward airspeed. Therefore, as a result of the relative wind
speed, the advancing blade side of the rotor disk can produce
more lift than the retreating blade side. [Figure 2-34]
indicated on a placard and marked on the airspeed indicator
by a red line.
Direction of Flight
Advancing Side
tion
Blade tip
speed
minus
helicopter
speed
(300 knots)
Blade tip
speed
plus
helicopter
speed
(500 knots)
Relative wind
a
rot
de
io
at
rot
n
Relative wind
Bl
a
Retreating Side
Blade
Forward flight at 100 knots
Figure 2-34. The blade tip speed of this helicopter is approximately
400 knots. If the helicopter is moving forward at 100 knots, the
relative windspeed on the advancing side is 400 knots. On the
retreating side, it is only 200 knots. This difference in speed causes
a dissymmetry of lift.
If this condition were allowed to exist, a helicopter with a
counterclockwise main rotor blade rotation would roll to the
left because of the difference in lift. In reality, the main rotor
blades flap and feather automatically to equalize lift across
the rotor disk. Articulated rotor systems, usually with three or
more blades, incorporate a horizontal hinge (flapping hinge)
to allow the individual rotor blades to move, or flap up and
down as they rotate. A semi-rigid rotor system (two blades)
utilizes a teetering hinge, which allows the blades to flap as
a unit. When one blade flaps up, the other blade flaps down.
As shown in Figure 2-35, as the rotor blade reaches the
advancing side of the rotor disk (A), it reaches its maximum
up flap velocity. When the blade flaps upward, the angle
between the chord line and the resultant relative wind
decreases. This decreases the AOA, which reduces the
amount of lift produced by the blade. At position (C), the
rotor blade is now at its maximum down flapping velocity.
Due to down flapping, the angle between the chord line and
the resultant relative wind increases. This increases the AOA
and thus the amount of lift produced by the blade.
The combination of blade flapping and slow relative wind
acting on the retreating blade normally limits the maximum
forward speed of a helicopter. At a high forward speed,
the retreating blade stalls because of a high AOA and slow
relative wind speed. This situation is called retreating blade
stall and is evidenced by a nose pitch up, vibration, and a
rolling tendency—usually to the left in helicopters with
counterclockwise blade rotation.
Pilots can avoid retreating blade stall by not exceeding the
never-exceed speed. This speed is designated VNE and is
Blade flapping compensates for dissymmetry of lift in the
following way. At a hover, equal lift is produced around the
rotor system with equal pitch (AOI) on all the blades and at
all points in the rotor system (disregarding compensation for
translating tendency). The rotor disk is parallel to the horizon.
To develop a thrust force, the rotor system must be tilted in
the desired direction of movement. Cyclic feathering changes
the angle of incidence differentially around the rotor system.
Forward cyclic movements decrease the angle of incidence
at one part on the rotor system while increasing the angle
in another part.
When transitioning to forward flight either from a hover or
taking off from the ground, pilots must be aware that as the
helicopter speed increases, translational lift becomes more
effective and causes the nose to rise, or pitch up (sometimes
referred to as blowback). This tendency is caused by the
combined effects of dissymmetry of lift and transverse flow.
Pilots must correct for this tendency to maintain a constant
rotor disk attitude that will move the helicopter through
the speed range in which blowback occurs. If the nose is
permitted to pitch up while passing through this speed range,
the aircraft may also tend to roll to the right. To correct for
this tendency, the pilot must continuously move the cyclic
forward as velocity of the helicopter increases until the
takeoff is complete and the helicopter has transitioned into
forward flight.
Figure 2-36 illustrates the changes in pitch angle as the cyclic
is moved forward at increased airspeeds. At a hover, the
cyclic is centered and the pitch angle on the advancing and
retreating blades is the same. At low forward speeds, moving
the cyclic forward reduces pitch angle on the advancing blade
and increases pitch angle on the retreating blade. This causes
a slight rotor tilt. At higher forward speeds, the pilot must
continue to move the cyclic forward. This further reduces
pitch angle on the advancing blade and further increases
pitch angle on the retreating blade. As a result, there is even
more tilt to the rotor than at lower speeds.
A horizontal lift component (thrust) generates higher
helicopter airspeed. The higher airspeed induces blade
flapping to maintain symmetry of lift. The combination of
flapping and cyclic feathering maintains symmetry of lift and
desired attitude on the rotor system and helicopter.
Translational Lift
Improved rotor efficiency resulting from directional flight
is called translational lift. The efficiency of the hovering
rotor system is greatly improved with each knot of incoming
2-19
B Angle of attack over nose
Chord lin
e
C Angle of attack at 9 o’clock position
Chord
Bl
a
Resultant relative wind
de
n
atio B
rot
A Angle of attack at 3 o’clock position
Chord
line
C
Downflap velocity
A
wind
Resultant relative
line
Resultant relati
ve wind
Upflap velocity
D
D Angle of attack over tail
Cho
rd lin
e
Relative wind
Angle of attack
Resultant relative wind
Figure 2-35. The combined upward flapping (reduced lift) of the advancing blade and downward flapping (increased lift) of the retreating
blade equalizes lift across the main rotor disk, counteracting dissymmetry of lift.
Effective Translational Lift (ETL)
Figure 2-36. To compensate for blowback, you must move the
cyclic forward.
wind gained by horizontal movement of the aircraft or
surface wind. As the incoming wind produced by aircraft
movement or surface wind enters the rotor system, turbulence
and vortices are left behind and the flow of air becomes
more horizontal. In addition, the tail rotor becomes more
aerodynamically efficient during the transition from hover
to forward flight. Figures 2-37 and 2-38 show the different
airflow patterns at different speeds and how airflow affects
the efficiency of the tail rotor.
2-20
While transitioning to forward flight at about 16 to 24 knots,
the helicopter goes through effective translational lift (ETL).
As mentioned earlier in the discussion on translational lift,
the rotor blades become more efficient as forward airspeed
increases. Between 16 and 24 knots, the rotor system
completely outruns the recirculation of old vortices and
begins to work in relatively undisturbed air. The flow of
air through the rotor system is more horizontal; therefore,
induced flow and induced drag are reduced. The AOA is
effectively increased, which makes the rotor system operate
more efficiently. This increased efficiency continues with
increased airspeed until the best climb airspeed is reached,
and total drag is at its lowest point.
As speed increases, translational lift becomes more effective,
nose rises or pitches up, and aircraft rolls to the right.
The combined effects of dissymmetry of lift, gyroscopic
precession, and transverse flow effect cause this tendency. It is
important to understand these effects and anticipate correcting
for them. Once the helicopter is transitioning through ETL,
the pilot needs to apply forward and left lateral cyclic input
to maintain a constant rotor-disk attitude. [Figure 2-39]
1–5 knots
ty
eloci
ard v
w
n
w
Do
r
of ai
e
m ol
su
c ul e
b
sed
y aft se
cti
on of ro
to
r
Figure 2-37. The airflow pattern for 1–5 knots of forward airspeed. Note how the downwind vortex is beginning to dissipate and induced
flow down through the rear of the rotor system is more horizontal.
Airflow pattern just prior to effective translational lift
10–15 knots
Figure 2-38. An airflow pattern at a speed of 10–15 knots. At this increased airspeed, the airflow continues to become more horizontal.
The leading edge of the downwash pattern is being overrun and is well back under the nose of the helicopter.
Translational Thrust
Translational thrust occurs when the tail rotor becomes more
aerodynamically efficient during the transition from hover
to forward flight. As the tail rotor works in progressively
less turbulent air, this improved efficiency produces more
antitorque thrust, causing the nose of the aircraft to yaw left
(with a main rotor turning counterclockwise) and forces the
pilot to apply right pedal (decreasing the AOA in the tail
rotor blades) in response. In addition, during this period, the
airflow affects the horizontal components of the stabilizer
found on most helicopters which tends to bring the nose of
the helicopter to a more level attitude.
When a helicopter is hovering, the tail rotor is operating in
very disturbed airflow. As the helicopter achieves ETL, the
tail rotor begins to generate much more thrust because of the
less disturbed airflow. The helicopter reacts to the increased
thrust by yawing. Therefore, as the helicopter achieves ETL,
you must reduce tail rotor thrust by pedal input at about the
same time that you need to make cyclic adjustments for lateral
tracking, acceleration, and climb.
Induced Flow
As the rotor blades rotate, they generate what is called
rotational relative wind. This airflow is characterized as
flowing parallel and opposite the rotor’s plane of rotation and
striking perpendicular to the rotor blade’s leading edge. This
rotational relative wind is used to generate lift. As rotor blades
produce lift, air is accelerated over the foil and projected
downward. Anytime a helicopter is producing lift, it moves
large masses of air vertically and down through the rotor
system. This downwash or induced flow can significantly
change the efficiency of the rotor system. Rotational relative
wind combines with induced flow to form the resultant
relative wind. As induced flow increases, resultant relative
wind becomes less horizontal. Since AOA is determined
2-21
More horizontal
flow of air
No recirculation
of air
Transverse flow effect is recognized by increased vibrations
of the helicopter at airspeeds just below ETL on takeoff and
after passing through ETL during landing. To counteract
transverse flow effect, a cyclic input to the left may be needed.
Sideward Flight
16–24 knots
Reduced induced flow
increases angle of attack
Tail rotor operates in
relatively clean air
Figure 2-39. Effective translational lift is easily recognized in actual
flight by a transient induced aerodynamic vibration and increased
performance of the helicopter.
by measuring the difference between the chord line and the
resultant relative wind, as the resultant relative wind becomes
less horizontal, AOA decreases. [Figure 2-40]
Transverse Flow Effect
As the helicopter accelerates in forward flight, induced flow
drops to near zero at the forward disk area and increases at
the aft disk area. These differences in lift between the fore and
aft portions of the rotor disk are called transverse flow effect.
[Figure 2-39] This increases the AOA at the front disk area
causing the rotor blade to flap up, and reduces AOA at the aft
disk area causing the rotor blade to flap down. Because the
rotor acts like a gyro, maximum displacement occurs 90° in the
direction of rotation. The result is a tendency for the helicopter to
roll slightly to the right as it accelerates through approximately
20 knots or if the headwind is approximately 20 knots.
In sideward flight, the tip-path plane is tilted in the direction
that flight is desired. This tilts the total lift-thrust vector
sideward. In this case, the vertical or lift component is still
straight up and weight straight down, but the horizontal or
thrust component now acts sideward with drag acting to the
opposite side. [Figure 2-41]
Sideward flight can be a very unstable condition due to the
parasitic drag of the fuselage combined with the lack of
horizontal stabilizer for that direction of flight. Increased
altitudes help with control and the pilot must always scan in
the direction of flight. Movement of the cyclic in the intended
direction of flight causes the helicopter to move, controls the
rate of speed, and ground track, but the collective and pedals
are key to successful sideward flight. Just as in forward flight,
the collective keeps the helicopter from contacting the ground
and the pedals help maintain the correct heading; even in
sideward flight, the tail of the helicopter should remain behind
you. Inputs to the cyclic should be smooth and controlled,
and the pilot should always be aware of the tip-path plane in
relation to the ground. [Figure 2-42]
Contacting the ground with the skids during sideward flight
will most likely result in a dynamic rollover event before the
pilot has a chance to react. Extreme caution should be used
Angle of attack
Angle of attack
Less induced flow
B
Resultant relative wind
Rotational relative wind
Greater induced flow
A
Resultant relative wind
Rotational relative wind
Downward velocity of air molecules used by aft section of rotor
More horizontal
flow of air
10–20 knots
A
B
Figure 2-40. A helicopter in forward flight, or hovering with a headwind or crosswind, has more molecules of air entering the aft portion
of the rotor blade. Therefore, the angle of attack is less and the induced flow is greater at the rear of the rotor disk.
2-22
Resultant
Resultant
Lift
Lift
Thrust
Thrust
Drag
Drag
Helicopter movement
Resultant
Figure 2-41. Forces acting on the helicopter during sideward flight.
when maneuvering the helicopter sideways to avoid such
hazards from happening. Refer to Chapter 11, Helicopter
Hazards and Emergencies.
Rearward Flight
For rearward flight, the tip-path plane is tilted rearward,
which, in turn, tilts the lift-thrust vector rearward. Drag now
acts forward with the lift component straight up and weight
straight down. [Figure 2-43]
Pilots must be aware of the hazards of rearward flight.
Because of the position of the horizontal stabilizer, the tail
end of the helicopter tends to pitch downward in rearward
flight, causing the probability of hitting the ground to be
greater than in forward flight. Another factor to consider
in rearward flight is skid design. Most helicopter skids are
not turned upward in the back, and any contact with the
ground during rearward flight can put the helicopter in an
Weight
Weight
Resultant
Downward force from
the horizontal stabilizer
Helicopter movement
Figure 2-43. Forces acting on the helicopter during rearward flight.
uncontrollable position leading to tail rotor contact with the
ground. Pilots must do a thorough scan of the area before
attempting to hover rearward, looking for obstacles and
terrain changes. Slower airspeeds can help mitigate risk and
maintain a higher-than-normal hover altitude.
Turning Flight
In forward flight, the rotor disk is tilted forward, which also
tilts the total lift-thrust force of the rotor disk forward. When
the helicopter is banked, the rotor disk is tilted sideward
resulting in lift being separated into two components. Lift
acting upward and opposing weight is called the vertical
component of lift. Lift acting horizontally and opposing
inertia (centrifugal force) is the horizontal component of lift
(centripetal force). [Figure 2-44]
Forward reference
Ground track required
Side reference
Figure 2-42. Forces acting on the helicopter during sideward flight.
2-23
rate of turn is higher. Simply put, collective pitch must be
increased in order to maintain altitude and airspeed while
turning. Collective pitch controls the angle of incidence and
along with other factors, determines the overall AOA in the
rotor system.
Centrifugal force
(horizontal component of lift)
Re
sul
tan
t lif
t
Vertical
component
of lift
Autorotation
70
80
90
0
60
20
10
Bank
angle
30
40
50
Weight
Centrifugal force (inertia)
Figure 2-44. Forces acting on the helicopter during turning flight.
As the angle of bank increases, the total lift force is tilted
more toward the horizontal, thus causing the rate of turn to
increase because more lift is acting horizontally. Since the
resultant lifting force acts more horizontally, the effect of
lift acting vertically is decreased. To compensate for this
decreased vertical lift, the AOA of the rotor blades must be
increased in order to maintain altitude. The steeper the angle
of bank is, the greater the AOA of the rotor blades required
to maintain altitude. Thus, with an increase in bank and a
greater AOA, the resultant lifting force increases and the
Autorotation is the state of flight where the main rotor system
of a helicopter is being turned by the action of air moving
up through the rotor rather than engine power driving the
rotor. In normal, powered flight, air is drawn into the main
rotor system from above and exhausted downward, but
during autorotation, air moves up into the rotor system from
below as the helicopter descends. Autorotation is permitted
mechanically by a freewheeling unit, which is a special clutch
mechanism that allows the main rotor to continue turning even
if the engine is not running. If the engine fails, the freewheeling
unit automatically disengages the engine from the main rotor
allowing the main rotor to rotate freely. It is the means by
which a helicopter can be landed safely in the event of an
engine failure; consequently, all helicopters must demonstrate
this capability in order to be certified. [Figure 2-45] If a
decision is made to attempt an engine restart in flight (the
parameters for this emergency procedure will be different for
each helicopter and must be precisely followed) the pilot must
reengage the engine starter switch to start the engine. Once
the engine is started, the freewheeling unit will reengage the
engine with the main rotor.
Hovering Autorotation
Most autorotations are performed with forward speed. For
simplicity, the following aerodynamic explanation is based
on a vertical autorotative descent (no forward speed) in still
air. Under these conditions, the forces that cause the blades
to turn are similar for all blades regardless of their position in
Autorotation
Dir
Direction of flight
ect
ion
of
fli
gh
t
Normal Powered Flight
Figure 2-45. During an autorotation, the upward flow of relative wind permits the main rotor blades to rotate at their normal speed. In
effect, the blades are “gliding” in their rotational plane.
2-24
the plane of rotation. Therefore, dissymmetry of lift resulting
from helicopter airspeed is not a factor.
During vertical autorotation, the rotor disk is divided into
three regions (as illustrated in Figure 2-46): driven region,
driving region, and stall region. Figure 2-47 shows three
blade sections that illustrate force vectors. Part A is the
driven region, B and D are points of equilibrium, part C is
the driving region, and part E is the stall region. Force vectors
are different in each region because rotational relative wind is
slower near the blade root and increases continually toward
the blade tip. Also, blade twist gives a more positive AOA in
the driving region than in the driven region. The combination
of the inflow up through the rotor with rotational relative
wind produces different combinations of aerodynamic force
at every point along the blade.
B
ation
rot
de
la
region 25
B
e
lad
Driv
The driving region, or autorotative region, normally lies
between 25 to 70 percent of the blade radius. Part C of
Figure 2-47 shows the driving region of the blade, which
produces the forces needed to turn the blades during
autorotation. Total aerodynamic force in the driving region is
inclined slightly forward of the axis of rotation, producing a
continual acceleration force. This inclination supplies thrust,
which tends to accelerate the rotation of the blade. Driving
region size varies with blade pitch setting, rate of descent,
and rotor rpm.
By controlling the size of this region, a pilot can adjust
autorotative rpm. For example, if the collective pitch is
raised, the pitch angle increases in all regions. This causes
the point of equilibrium to move inboard along the blade’s
span, thus increasing the size of the driven region. The stall
region also becomes larger while the driving region becomes
smaller. Reducing the size of the driving region causes the
acceleration force of the driving region and rpm to decrease.
A constant rotor rpm is achieved by adjusting the collective
pitch so blade acceleration forces from the driving region
are balanced with the deceleration forces from the driven
and stall regions.
%
a
rot
tion
St
a ll
equilibrium, TAF is aligned with the axis of rotation. Lift
and drag are produced, but the total effect produces neither
acceleration nor deceleration.
ing region 45%
Driven region 30%
Figure 2-46. Blade regions during autorotational descent.
The driven region, also called the propeller region, is nearest
the blade tips. Normally, it consists of about 30 percent of the
radius. In the driven region, part A of Figure 2-47, the total
aerodynamic force (TAF) acts behind the axis of rotation,
resulting in an overall drag force. The driven region produces
some lift, but that lift is offset by drag. The overall result is
a deceleration in the rotation of the blade. The size of this
region varies with the blade pitch, rate of descent, and rotor
rpm. When changing autorotative rpm blade pitch, or rate of
descent, the size of the driven region in relation to the other
regions also changes.
There are two points of equilibrium on the blade—one
between the driven region and the driving region, and one
between the driving region and the stall region. At points of
The inner 25 percent of the rotor blade is referred to as the
stall region and operates above its maximum AOA (stall
angle), causing drag, which tends to slow rotation of the
blade. Part E of Figure 2-48 depicts the stall region.
Autorotation (Forward Flight)
Autorotative force in forward flight is produced in exactly the
same manner as when the helicopter is descending vertically
in still air. However, because forward speed changes the
inflow of air up through the rotor disk, all three regions move
outboard along the blade span on the retreating side of the
disk where AOA is larger. [Figure 2-48] With lower AOA
on the advancing side blade, more of the blade falls in the
driven region. On the retreating side, more of the blade is in
the stall region. A small section near the root experiences a
reversed flow; therefore, the size of the driven region on the
retreating side is reduced.
Prior to landing from an autorotative descent (or autorotation),
the pilot must flare the helicopter in order to decelerate. The
pilot initiates the flare by applying aft cyclic. As the helicopter
flares back, the airflow patterns change around the blades
causing the rpm to increase. Pilots must adjust the collective
as necessary to keep the rpm within operating limits.
2-25
TAF
A
Driven region
Lift
A
Drag
Total
aerodynamic
force aft of
axis of rotation
Rotational
relative
wind
AOA = 2°
Drag
Driven region
RW
Resultant
Inflow up through rotor
TAF
B&D
Point of equilibrium
Chord line
Lift
B
Autorotative force
Equilibrium
Drag
Inflow
C
Driving region
TAF
C
Lift
Total aerodynamic
force forward of
axis of rotation
AOA = 6°
Driving region
Point of equilibrium
Drag
D
Inflow
E
Stall region
Axis of rotation
E
AOA = 24°
(blade is stalled)
Lift TAF
Drag
Drag
Inflow
Figure 2-47. Force vectors in vertical autorotation descent.
2-26
Stall region
Direction of Flight
Advancing side
Retreating side
B
ation
rot
de
la
B
e
lad
a
rot
tion
St
a ll
region
Driv
ing region
Driven region
Figure 2-48. Blade regions in forward autorotation descent.
Chapter Summary
This chapter introduced the basics of aerodynamic
fundamentals and theory and how they relate to flying a
helicopter. This chapter also explained how aerodynamics
affect helicopter flight and how important it is for pilots to
understand aerodynamic principles and be prepared to react
to these effects. For additional information on aerodynamics,
refer to the aerodynamics of flight portion of the Pilot’s
Handbook of Aeronautical Knowledge.
2-27
2-28
Chapter 3
Helicopter Flight Controls
Introduction
There are three major controls in a helicopter that the pilot
must use during flight. They are the collective pitch control,
the cyclic pitch control, and the antitorque pedals or tail rotor
control. In addition to these major controls, the pilot must also
use the throttle control, which is usually mounted directly
to the collective pitch control in order to fly the helicopter.
In this chapter, the control systems described are not limited
to the single main rotor type helicopter but are employed
in one form or another in most helicopter configurations.
All examples in this chapter refer to a counterclockwise
main rotor blade rotation as viewed from above. If flying a
helicopter with a clockwise rotation, left and right references
must be reversed, particularly in the areas of rotor blade pitch
change, antitorque pedal movement, and tail rotor thrust.
3-1
Collective Pitch Control
Throttle Control
The collective pitch control (or simply “collective” or “thrust
lever”) is located on the left side of the pilot’s seat and is
operated with the left hand. The collective is used to make
changes to the pitch angle of the main rotor blades and does
this simultaneously, or collectively, as the name implies. As
the collective pitch control is raised, there is a simultaneous
and equal increase in pitch angle of all main rotor blades;
as it is lowered, there is a simultaneous and equal decrease
in pitch angle. This is done through a series of mechanical
linkages and the amount of movement in the collective lever
determines the amount of blade pitch change. [Figure 3-1]
An adjustable friction control helps prevent inadvertent
collective pitch movement.
The function of the throttle is to regulate engine rpm. If
the correlator or governor system does not maintain the
desired rpm when the collective is raised or lowered, or if
those systems are not installed, the throttle must be moved
manually with the twist grip in order to maintain rpm. The
throttle control is much like a motorcycle throttle, and works
in virtually the same way. Twisting the throttle to the left
increases rpm; twisting the throttle to the right decreases
rpm. [Figure 3-2]
Changing the pitch angle on the blades changes the angle
of incidence on each blade. With a change in angle of
incidence comes a change in drag, which affects the speed
or revolutions per minute (rpm) of the main rotor. As the
pitch angle increases, angle of incidence increases, drag
increases, and rotor rpm decreases. Decreasing pitch angle
decreases both angle of incidence and drag, while rotor rpm
increases. In order to maintain a constant rotor rpm, which
is essential in helicopter operations, a proportionate change
in power is required to compensate for the change in drag.
This is accomplished with the throttle control or governor,
which automatically adjusts engine power.
Governor/Correlator
A governor is a sensing device that senses rotor and engine
rpm and makes the necessary adjustments in order to keep
rotor rpm constant. In normal operations, once the rotor
rpm is set, the governor keeps the rpm constant, and there
is no need to make any throttle adjustments. Governors are
common on all turbine helicopters (as it is a function of the
fuel control system of the turbine engine), and used on some
piston powered helicopters.
A correlator is a mechanical connection between the
collective lever and the engine throttle. When the collective
lever is raised, power is automatically increased; when
lowered, power is decreased. This system maintains rpm
close to the desired value, but still requires adjustment of
the throttle for fine tuning.
Figure 3-1. Raising the collective pitch control increases the pitch angle, or angle of incidence, by the same amount on all blades.
3-2
Twist grip throttle
Figure 3-2. A twist grip throttle is usually mounted on the end of
the collective lever. The throttles on some turbine helicopters are
mounted on the overhead panel or on the floor in the cockpit.
Some helicopters do not have correlators or governors and
require coordination of all collective and throttle movements.
When the collective is raised, the throttle must be increased;
when the collective is lowered, the throttle must be decreased.
As with any aircraft control, large adjustments of either
collective pitch or throttle should be avoided. All corrections
should be made through the use of smooth pressure.
In piston helicopters, the collective pitch is the primary control
for manifold pressure, and the throttle is the primary control
for rpm. However, the collective pitch control also influences
rpm, and the throttle also influences manifold pressure;
therefore, each is considered to be a secondary control of the
other’s function. Both the tachometer (rpm indicator) and
the manifold pressure gauge must be analyzed to determine
which control to use. Figure 3-3 illustrates this relationship.
if rpm is
and manifold
pressure is
LOW
LOW
Increasing the throttle increases
manifold pressure and rpm
LOW
HIGH
Lowering the collective pitch
decreases manifold pressure
and increases rpm
HIGH
LOW
Raising the collective pitch
increases manifold pressure and
decreases rpm
HIGH
HIGH
Reducing the throttle decreases
manifold pressure and rpm
control allows the pilot to fly the helicopter in any direction
of travel: forward, rearward, left, and right. As discussed
in Chapter 3, Aerodynamics of Flight, the total lift force is
always perpendicular to the tip-path plane of the main rotor.
The purpose of the cyclic pitch control is to tilt the tip-path
plane in the direction of the desired horizontal direction. The
cyclic controls the rotor disk tilt versus the horizon, which
directs the rotor disk thrust to enable the pilot to control the
direction of travel of the helicopter.
The rotor disk tilts in the same direction the cyclic pitch control
is moved. If the cyclic is moved forward, the rotor disk tilts
forward; if the cyclic is moved aft, the disk tilts aft, and so on.
Because the rotor disk acts like a gyro, the mechanical linkages
for the cyclic control rods are rigged in such a way that they
decrease the pitch angle of the rotor blade approximately
90° before it reaches the direction of cyclic displacement,
and increase the pitch angle of the rotor blade approximately
90° after it passes the direction of displacement. An increase
in pitch angle increases AOA; a decrease in pitch angle
decreases AOA. For example, if the cyclic is moved forward,
the AOA decreases as the rotor blade passes the right side of
the helicopter and increases on the left side. This results in
Cyclic pitch control
Solution
Cyclic pitch control
Figure 3-3. Relationship between rpm, manifold pressure, collective,
and throttle.
Cyclic Pitch Control
The cyclic pitch control is usually projected upward from
the cockpit floor, between the pilot’s legs or between the two
pilot seats in some models. [Figure 3-4] This primary flight
Figure 3-4. The cyclic pitch control may be mounted vertically
between the pilot’s knees or on a teetering bar from a single cyclic
located in the center of the helicopter. The cyclic can pivot in all
directions.
3-3
maximum downward deflection of the rotor blade in front
of the helicopter and maximum upward deflection behind it,
causing the rotor disk to tilt forward.
Antitorque Pedals
The antitorque pedals, located on the cabin floor by the pilot’s
feet, control the pitch and therefore the thrust of the tail rotor
blades or other antitorque system. See Chapter 5, Helicopter
Components, Sections, and Systems, for a discussion on
these other systems. [Figure 3-5] Newton’s Third Law was
discussed in Chapter 2, General Aerodynamics, stating that
for every action there is an equal and opposite reaction.
This law applies to the helicopter fuselage and its rotation
in the opposite direction of the main rotor blades unless
counteracted and controlled. To make flight possible and
to compensate for this torque, most helicopter designs
incorporate an antitorque rotor or tail rotor. The antitorque
pedals allow the pilot to control the pitch angle of the tail
rotor blades, which in forward flight puts the helicopter in
longitudinal trim and, while at a hover, enables the pilot to
turn the helicopter 360°. The antitorque pedals are connected
to the pitch change mechanism on the tail rotor gearbox and
allow the pitch angle on the tail rotor blades to be increased
or decreased.
At speeds above translational lift, the pedals are used to
compensate for torque to put the helicopter in longitudinal
trim so that coordinated flight can be maintained. The cyclic
control is used to change heading by making a turn to the
desired direction.
The thrust of the tail rotor depends on the pitch angle of the
tail rotor blades. This pitch angle can be positive, negative,
or zero. A positive pitch angle tends to move the tail to the
right. A negative pitch angle moves the tail to the left, while
no thrust is produced with a zero pitch angle. The maximum
positive pitch angle of the tail rotor is generally greater than
the maximum negative pitch angle available. This is because
the primary purpose of the tail rotor is to counteract the torque
of the main rotor. The capability for tail rotors to produce
thrust to the left (negative pitch angle) is necessary, because
during autorotation the drag of the transmission tends to yaw
the nose to the left, or in the same direction the main rotor
is turning.
From the neutral position, applying right pedal causes the
nose of the helicopter to yaw right and the tail to swing to
the left. Pressing on the left pedal has the opposite effect:
the nose of the helicopter yaws to the left and the tail swings
right. [Figure 3-6]
With the antitorque pedals in the neutral position, the tail rotor
has a medium positive pitch angle. In medium positive pitch,
the tail rotor thrust approximately equals the torque of the
main rotor during cruise flight, so the helicopter maintains
a constant heading in level flight.
A vertical fin or stabilizer is used in many single-rotor
helicopters to help aid in heading control. The fin is designed
to optimize directional stability in flight with a zero tail rotor
thrust setting. The size of the fin is crucial to this design. If
the surface is too large, the tail rotor thrust may be blocked.
Heading control would be more difficult at slower airspeeds
and at a hover and the vertical fin would then weathervane.
Figure 3-5. Antitorque pedals compensate for changes in torque
and control heading in a hover.
Heading Control
The tail rotor is used to control the heading of the helicopter
while hovering or when making hovering turns, as well as
counteracting the torque of the main rotor. Hovering turns
are commonly referred to as “pedal turns.”
3-4
Helicopters that are designed with tandem rotors do not have
an antitorque rotor. The helicopter is designed with both
rotor systems rotating in opposite directions to counteract the
torque rather than a tail rotor. Directional antitorque pedals
are used for directional control of the aircraft while in flight,
as well as while taxiing with the forward gear off the ground.
il
Ta
m
ov
es
High Positive Pitch
ov
es
Medium Positive Pitch
il
Ta
m
Negative or Low Positive Pitch
Figure 3-6. Tail rotor pitch angle and thrust in relation to pedal positions during cruising flight.
In intermeshing rotor systems, which are a set of two rotors
turning in opposite directions with each rotor mast mounted
on the helicopter with a slight angle to the other so that
the blades intermesh without colliding, and a coaxial rotor
systems, which are a pair of rotors mounted one above the
other on the same shaft and turning in opposite directions, the
heading pedals control the heading of the helicopter while at
a hover by imbalancing torque between the rotors, allowing
for the torque to turn the helicopter.
Chapter Summary
This chapter introduced the pilot to the major flight controls
and how they work in relation to each other. The chapter also
correlates the use of flight controls and aerodynamics and
how the two work together to make flight possible.
3-5
3-6
Chapter 4
Helicopter Components,
Sections, and Systems
Introduction
This chapter discusses the components, sections, and systems
found on most modern helicopters. Helicopters come in a
variety of sizes and shapes, but most share the same major
components. The chapter introduces the major components/
sections of the helicopter and the systems that correlate
with each. Knowing how the components and systems
work on the helicopter enables the pilot to more easily
recognize malfunctions and possible emergency situations.
Understanding the relationship of these systems allows the
pilot to make an informed decision and take the appropriate
corrective action should a problem arise.
Airframe
The airframe, or fundamental structure, of a helicopter can be
made of either metal, wood, or composite materials, or some
combination of the two. Typically, a composite component
consists of many layers of fiber-impregnated resins, bonded
to form a smooth panel. Tubular and sheet metal substructures
are usually made of aluminum, though stainless steel or
titanium are sometimes used in areas subject to higher
stress or heat. Airframe design encompasses engineering,
aerodynamics, materials technology, and manufacturing
methods to achieve favorable balances of performance,
reliability, and cost. [Figure 4-1]
4-1
Fuselage
The fuselage, the outer core of the airframe, is an aircraft’s
main body section that houses the cabin which holds the crew,
passengers, and cargo. Helicopter cabins have a variety of
seating arrangements. Most have the pilot seated on the right
side, although there are some with the pilot seated on the
left side or center. The fuselage also houses the engine, the
transmission, avionics, flight controls, and the powerplant.
[Figure 4-1]
Main Rotor System
The rotor system is the rotating part of a helicopter which
generates lift. The rotor consists of a mast, hub, and rotor
blades. The mast is a hollow cylindrical metal shaft which
extends upwards from and is driven and sometimes supported
by the transmission. At the top of the mast is the attachment
point for the rotor blades called the hub. The rotor blades are
then attached to the hub by any number of different methods.
Main rotor systems are classified according to how the main
rotor blades are attached and move relative to the main rotor
hub. There are three basic classifications: semirigid, rigid,
or fully articulated. Some modern rotor systems, such as the
bearingless rotor system, use an engineered combination of
these types.
Semirigid Rotor System
A semirigid rotor system is usually composed of two blades
that are rigidly mounted to the main rotor hub. The main
rotor hub is free to tilt with respect to the main rotor shaft on
what is known as a teetering hinge. This allows the blades to
flap together as a unit. As one blade flaps up, the other flaps
down. Since there is no vertical drag hinge, lead/lag forces
are absorbed and mitigated by blade bending. The semirigid
rotor is also capable of feathering, which means that the
pitch angle of the blade changes. This is made possible by
the feathering hinge. [Figure 4-2]
The underslung rotor system mitigates the lead/lag forces
by mounting the blades slightly lower than the usual plane
of rotation, so the lead and lag forces are minimized. As the
blades cone upward, the center of pressures of the blades are
almost in the same plane as the hub. Whatever stresses are
remaining bend the blades for compliance.
If the semirigid rotor system is an underslung rotor, the center
of gravity (CG) is below where it is attached to the mast. This
underslung mounting is designed to align the blade’s center
of mass with a common flapping hinge so that both blades’
centers of mass vary equally in distance from the center of
rotation during flapping. The rotational speed of the system
Main rotor system
Tail rotor system
Airframe
Transmission
Fuselage
Powerplant
Landing gear
Figure 4-1. The major components of a helicopter are the airframe, fuselage, landing gear, powerplant, transmission, main rotor system,
and tail rotor system.
4-2
Static stops
Teetering hinge
Pitch horn
Feathering hinge
Main rotor mast
Figure 4-2. The teetering hinge allows the main rotor hub to tilt, and
the feathering hinge enables the pitch angle of the blades to change.
tends to change, but this is restrained by the inertia of the
engine and flexibility of the drive system. Only a moderate
amount of stiffening at the blade root is necessary to handle
this restriction. Simply put, underslinging effectively
eliminates geometric imbalance.
Helicopters with semirigid rotors are vulnerable to a
condition known as mast bumping which can cause the rotor
Main rotor hub
flap stops to shear the mast. The mechanical design of the
semirigid rotor system dictates downward flapping of the
blades must have some physical limit. Mast bumping is the
result of excessive rotor flapping. Each rotor system design
has a maximum flapping angle. If flapping exceeds the design
value, the static stop will contact the mast. It is the violent
contact between the static stop and the mast during flight
that causes mast damage or separation. This contact must
be avoided at all costs.
Mast bumping is directly related to how much the blade
system flaps. In straight and level flight, blade flapping is
minimal, perhaps 2° under usual flight conditions. Flapping
angles increase slightly with high forward speeds, at low
rotor rpm, at high-density altitudes, at high gross weights, and
when encountering turbulence. Maneuvering the aircraft in a
sideslip or during low-speed flight at extreme CG positions
can induce larger flapping angles.
Rigid Rotor System
The rigid rotor system shown in Figure 4-3 is mechanically
simple, but structurally complex because operating loads
must be absorbed in bending rather than through hinges. In
this system, the blade roots are rigidly attached to the rotor
hub. Rigid rotor systems tend to behave like fully articulated
systems through aerodynamics, but lack flapping or lead/
lag hinges. Instead, the blades accommodate these motions
Blade pitch horns
Main rotor blades
Pitch change links
Main rotor blades
Main rotor mast
Figure 4-3. Four-blade hingeless (rigid) main rotor. Rotor blades are comprised of glass fiber reinforced material. The hub is a single
piece of forged rigid titanium.
4-3
System Type
Advantages
Articulated
Good control
response
Semirigid
(Teetering,
Underslung, or
See-Saw)
Simple, easy to
hangar due to two
blades
Rigid
Simple design,
crisp response
n
ositio
ing p
ition
Rotor blade
Lagg
There are several variations of the basic three rotor head
designs. The bearingless rotor system is closely related to
the articulated rotor system, but has no bearings or hinges.
This design relies on the structure of blades and hub to absorb
stresses. The main difference between the rigid rotor system
and the bearingless system is that the bearingless system has
no feathering bearing—the material inside the cuff is twisted
by the action of the pitch change arm. Nearly all bearingless
rotor hubs are made of fiber-composite materials. The
differences in handling between the types of rotor system
are summarized in Figure 4-4.
Pure Radial Position
g pos
The rigid rotor system is very responsive and is usually not
susceptible to mast bumping like the semirigid or articulated
systems because the rotor hubs are mounted solid to the main
rotor mast. This allows the rotor and fuselage to move together
as one entity and eliminates much of the oscillation usually
present in the other rotor systems. Other advantages of the rigid
rotor include a reduction in the weight and drag of the rotor
hub and a larger flapping arm, which significantly reduces
control inputs. Without the complex hinges, the rotor system
becomes much more reliable and easier to maintain than the
other rotor configurations. A disadvantage of this system is
the quality of ride in turbulent or gusty air. Because there are
no hinges to help absorb the larger loads, vibrations are felt
in the cabin much more than with other rotor head designs.
Fully Articulated Rotor System
Fully articulated rotor systems allow each blade to lead/lag
(move back and forth in plane), flap (move up and down
about an inboard mounted hinge) independent of the other
blades, and feather (rotate about the pitch axis to change lift).
[Figures 4-5 and 4-6] Each of these blade motions is related
Leadin
by bending. They cannot flap or lead/lag, but they can be
feathered. As advancements in helicopter aerodynamics
and materials continue to improve, rigid rotor systems may
become more common because the system is fundamentally
easier to design and offers the best properties of both
semirigid and fully articulated systems.
Disadvantages
High aerodynamic
drag. More complex,
greater cost.
Reaction to control
input not as quick
as articulated head.
Vibration can be
higher than multibladed articulated
systems.
Lead/lag hinge
(Vertical hinge)
Higher vibration than
articulated rotor.
Figure 4-4. Differences in handling between the types of rotor
Rotor hub
Center of rotation
system.
Figure 4-5. Lead/lag hinge allows the rotor blade to move back
and forth in plane.
4-4
Pitch change axis (feathering)
Pitch horn
Figure 4-6. Fully
articulated flapping hub.
Flapping hinge
Drag hinge
to the others. Fully articulated rotor systems are found on
helicopters with more than two main rotor blades.
As the rotor spins, each blade responds to inputs from the
control system to enable aircraft control. The center of lift
on the whole rotor system moves in response to these inputs
to effect pitch, roll, and upward motion. The magnitude of
this lift force is based on the collective input, which changes
pitch on all blades in the same direction at the same time. The
location of this lift force is based on the pitch and roll inputs
from the pilot. Therefore, the feathering angle of each blade
(proportional to its own lifting force) changes as it rotates
with the rotor, hence the name “cyclic control.”
Le
ad
in
g
po
sit
io
n
As the lift on a given blade increases, it tends to flap upwards.
The flapping hinge for the blade permits this motion and is
balanced by the centrifugal force of the weight of the blade,
which tries to keep it in the horizontal plane. [Figure 4-7]
Lead/lag or drag hinge
ition
g pos
in
Lagg
Figure 4-7. Fully articulated rotor blade with flapping hinge.
Either way, some motion must be accommodated. The
centrifugal force is nominally constant; however, the flapping
force is affected by the severity of the maneuver (rate of
climb, forward speed, aircraft gross weight). As the blade
flaps, its CG changes. This changes the local moment of
inertia of the blade with respect to the rotor system and it
speeds up or slows down with respect to the rest of the blades
and the whole rotor system. This is accommodated by the
lead/lag or drag hinge, shown in Figure 4-8, and is easier to
visualize with the classical ‘ice skater doing a spin’ image.
As the skater moves her arms in, she spins faster because her
Damper
Figure 4-8. Drag hinge.
inertia changes but her total energy remains constant (neglect
friction for purposes of this explanation). Conversely, as
her arms extend, her spin slows. This is also known as the
conservation of angular momentum. An in-plane damper
typically moderates lead/lag motion.
So, following a single blade through a single rotation
beginning at some neutral position, as load increases from
increased feathering, it flaps up and leads forward. As it
continues around, it flaps down and lags backward. At the
lowest point of load, it is at its lowest flap angle and also at
its most ‘rearward’ lag position. Because the rotor is a large,
rotating mass, it behaves somewhat like a gyroscope. The
effect of this is that a control input is usually realized on
the attached body at a position 90° prior to the control input
displacement in the axis of rotation. This is accounted for
by the designers through placement of the control input to
the rotor system so that a forward input of the cyclic control
stick results in a nominally forward motion of the aircraft.
The effect is made transparent to the pilot.
Older hinge designs relied on conventional metal bearings. By
basic geometry, this precludes a coincident flapping and lead/
lag hinge and is cause for recurring maintenance. Newer rotor
systems use elastomeric bearings, arrangements of rubber
and steel that can permit motion in two axes. Besides solving
some of the above-mentioned kinematic issues, these bearings
are usually in compression, can be readily inspected, and
eliminate the maintenance associated with metallic bearings.
Elastomeric bearings are naturally fail-safe and their wear
is gradual and visible. The metal-to-metal contact of older
bearings and the need for lubrication is eliminated in this design.
4-5
The stationary swash plate is mounted around the main rotor
mast and connected to the cyclic and collective controls by a
series of pushrods. It is restrained from rotating by an antidrive link but can tilt in all directions and move vertically.
The rotating swash plate is mounted to the stationary swash
plate by means of a uniball sleeve. It is connected to the mast
by drive links and must rotate in constant relationship with
the main rotor mast. Both swash plates tilt and slide up and
down as one unit. The rotating swash plate is connected to
the pitch horns by the pitch links.
Freewheeling Unit
Figure 4-9. Tandem rotor heads.
Tandem Rotor
Tandem rotor (sometimes referred to as dual rotor)
helicopters have two large horizontal rotor assemblies; a
twin rotor system, instead of one main assembly, and a
smaller tail rotor. [Figure 5-9] Single rotor helicopters need
an anti-torque system to neutralize the twisting momentum
produced by the single large rotor. Tandem rotor helicopters,
however, use counter-rotating rotors, with each canceling
out the other’s torque. Counter-rotating rotor blades will not
collide with and destroy each other if they flex into the other
rotor’s pathway. This configuration also has the advantage
of being able to hold more weight with shorter blades, since
there are two sets. Also, all of the power from the engines can
be used for lift, whereas a single rotor helicopter uses power
to counter the torque.
Since lift in a helicopter is provided by rotating airfoils,
these airfoils must be free to rotate if the engine fails. The
freewheeling unit automatically disengages the engine from
the main rotor when engine revolutions per minute (rpm)
is less than main rotor rpm. [Figure 4-11] This allows the
main rotor and tail rotor to continue turning at normal inflight speeds. The most common freewheeling unit assembly
consists of a one-way sprag clutch located between the engine
and main rotor transmission. This is usually in the upper
pulley in a piston helicopter or mounted on the accessory
gearbox in a turbine helicopter. When the engine is driving
the rotor, inclined surfaces in the sprag clutch force rollers
against an outer drum. This prevents the engine from
Swash Plate Assembly
The purpose of the swash plate is to convert stationary
control inputs from the pilot into rotating inputs which can be
connected to the rotor blades or control surfaces. It consists
of two main parts: stationary swash plate and rotating swash
plate. [Figure 4-10]
Inner and outer parts turning at same rpm
Pitch link
Stationary swash plate
Drive link
Rotating swash plate
Control rod
Figure 4-10. Stationary and rotating swash plate.
4-6
Outer turning much faster than inner
Figure 4-11. Freewheeling unit in normal drive position and
freewheeling position.
exceeding transmission rpm. If the engine fails, the rollers
move inward, allowing the outer drum to exceed the speed
of the inner portion. The transmission can then exceed the
speed of the engine. In this condition, engine speed is less
than that of the drive system, and the helicopter is in an
autorotative state.
Antitorque System
Helicopters with a single, main rotor system require a
separate antitorque system. This is most often accomplished
through a variable pitch, antitorque rotor or tail rotor.
[Figure 4-12] Pilots vary the thrust of the antitorque system to
maintain directional control whenever the main rotor torque
changes, or to make heading changes while hovering. Most
helicopters drive the tail rotor shaft from the transmission
to ensure tail rotor rotation (and hence control) in the event
that the engine quits. Usually, negative antitorque thrust is
needed in autorotations to overcome transmission friction.
d
Bla
e rot
ation
Tor
qu
e
Figure 4-13. Fenestron or “fan-in-tail” antitorque system. This
design provides an improved margin of safety during ground
operations.
flying in the downwash of the rotor system, producing up to
60 percent of the antitorque required in a hover. The balance
of the directional control is accomplished by a rotating direct
jet thruster. In forward flight, the vertical stabilizers provide
the majority of the antitorque; however, directional control
remains a function of the direct jet thruster. The NOTAR
antitorque system eliminates some of the mechanical
disadvantages of a tail rotor, including long drive shafts,
hanger bearings, intermediate gearboxes and 90° gearboxes.
[Figure 4-14]
tion
Blade rota
Downwash
Tor
qu
e
Tail rotor thrust
to compensate
for torque
Air jet
Main rotor wake
Lift
Figure 4-12. Antitorque rotor produces thrust to oppose torque.
Fenestron
Another form of antitorque system is the fenestron or “fanin-tail” design. This system uses a series of rotating blades
shrouded within a vertical tail. Because the blades are located
within a circular duct, they are less likely to come into contact
with people or objects. [Figure 4-13]
NOTAR®
Using the natural characteristics of helicopter aerodynamics,
the NOTAR antitorque system provides safe, quiet,
responsive, foreign object damage (FOD) resistant directional
control. The enclosed variable-pitch composite blade fan
produces a low pressure, high volume of ambient air to
pressurize the composite tailboom. The air is expelled
through two slots which run the length of the tailboom on the
right side, causing a boundary-layer control called the Coanda
effect. The result is that the tailboom becomes a “wing,”
Air intake
Rotating nozzle
Figure 4-14. While in a hover, Coanda effect supplies approximately
two-thirds of the lift necessary to maintain directional control.
The rest is created by directing the thrust from the controllable
rotating nozzle.
4-7
Antitorque Drive Systems
The antitorque drive system consists of an antitorque drive
shaft and a antitorque transmission mounted at the end of the
tail boom. The drive shaft may consist of one long shaft or a
series of shorter shafts connected at both ends with flexible
couplings. This allows the drive shaft to flex with the tail
boom. The tail rotor transmission provides a right angle drive
for the tail rotor and may also include gearing to adjust the
output to optimum tail rotor rpm. [Figure 4-15] Tail rotors
may also have an intermediate gearbox to turn the power up
a pylon or vertical fin.
Engines
Reciprocating Engines
Reciprocating engines, also called piston engines, are
generally used in smaller helicopters. Most training
helicopters use reciprocating engines because they are
relatively simple and inexpensive to operate. Refer to the
Pilot’s Handbook of Aeronautical Knowledge for a detailed
explanation and illustrations of the piston engine.
Turbine Engines
Turbine engines are more powerful and are used in a wide
variety of helicopters. They produce a tremendous amount
of power for their size but are generally more expensive
to operate. The turbine engine used in helicopters operates
differently from those used in airplane applications. In most
applications, the exhaust outlets simply release expended
gases and do not contribute to the forward motion of the
helicopter. Approximately 75 percent of the incoming airflow
is used to cool the engine.
The gas turbine engine mounted on most helicopters is
made up of a compressor, combustion chamber, turbine,
and accessory gearbox assembly. The compressor draws
filtered air into the plenum chamber and compresses it.
Common type filters are centrifugal swirl tubes where debris
is ejected outward and blown overboard prior to entering
the compressor, or engine barrier filters (EBF), similar to
the K&N filter element used in automotive applications.
Although this design significantly reduces the ingestion of
FOD, it is important for pilots to be aware of how much
debris is actually being filtered. Operating in the sand, dust,
or even in grassy type materials can choke an engine in just
minutes. The compressed air is directed to the combustion
section through discharge tubes where atomized fuel is
injected into it. The fuel/air mixture is ignited and allowed
to expand. This combustion gas is then forced through a
series of turbine wheels causing them to turn. These turbine
wheels provide power to both the engine compressor and the
accessory gearbox. Depending on model and manufacturer,
the rpm range can vary from a range low of 20,000 to a range
high of 51,600.
Power is provided to the main rotor and tail rotor systems
through the freewheeling unit which is attached to the
accessory gearbox power output gear shaft. The combustion
gas is finally expelled through an exhaust outlet. The
temperature of gas is measured at different locations and is
referenced differently by each manufacturer. Some common
terms are: inter-turbine temperature (ITT), exhaust gas
temperature (EGT), or turbine outlet temperature (TOT).
TOT is used throughout this discussion for simplicity
purposes. [Figure 4-16]
Compressor
The compressor may consist of an axial compressor, a
centrifugal compressor, or combination of the two. An axial
compressor consists of two main elements: the rotor and the
stator. The rotor consists of a number of blades fixed on a
rotating spindle and resembles a fan. As the rotor turns, air is
Input drives sun wheel
Tail rotor drive shaft
Tail rotor
Tail rotor transmission
Main transmission
Power and accessory gearbox
Main drive shaft with freewheeling unit
Figure 4-15. The tail rotor driveshaft is connected to both the main transmission and the tail rotor transmission.
4-8
Compression Section
Gearbox
Section
Exhaust air outlet
Turbine Section
N2 Rotor
Stator
Combustion Section
N1 Rotor
Compressor rotor
Igniter plug
Air inlet
Fuel nozzle
Inlet air
Compressor discharge air
Combustion gases
Exhaust gases
Gear
Output Shaft
Combustion liner
Figure 4-16. Many helicopters use a turboshaft engine to drive the main transmission and rotor systems. The main difference between
a turboshaft and a turbojet engine is that most of the energy produced by the expanding gases is used to drive a turbine rather than
producing thrust through the expulsion of exhaust gases.
drawn inward. Stator vanes are arranged in fixed rows between
the rotor blades and act as a diffuser at each stage to decrease
air velocity and increase air pressure. There may be a number
of rows of rotor blades and stator vanes. Each row constitutes a
pressure stage, and the number of stages depends on the amount
of air and pressure rise required for the particular engine.
A centrifugal compressor consists of an impeller, diffuser,
and a manifold. The impeller, which is a forged disc with
integral blades, rotates at a high speed to draw air in and
expel it at an accelerated rate. The air then passes through
the diffuser, which slows the air down. When the velocity
of the air is slowed, static pressure increases, resulting
in compressed, high pressure air. The high pressure air
then passes through the compressor manifold where it is
distributed to the combustion chamber via discharge tubes.
If the airflow through the compressor is disturbed, a condition
called surge, or compressor stall, may take effect. This
phenomenon is a periodic stalling of the compressor blades.
When this occurs, the pressure at the compressor is reduced
and the combustion pressure may cause reverse flow into the
compressor output. As the airflow through the compressor is
reduced, the air pressure then increases temporarily correcting
the condition until it occurs again. This is felt throughout the
airframe as vibrations and is accompanied by power loss
and an increase in turbine outlet temperature (TOT) as the
fuel control adds fuel in an attempt to maintain power. This
condition may be corrected by activating the bleed air system
which vents excess pressure to the atmosphere and allows
a larger volume of air to enter the compressor to unstall the
compressor blades.
Combustion Chamber
Unlike a piston engine, the combustion in a turbine engine is
continuous. An igniter plug serves only to ignite the fuel/air
mixture when starting the engine. Once the fuel/air mixture
is ignited, it continues to burn as long as the fuel/air mixture
continues to be present. If there is an interruption of fuel, air,
or both, combustion ceases. This is known as a “flameout,”
and the engine must be restarted or re-lit. Some helicopters
are equipped with auto-relight, which automatically activates
the igniters to start combustion if the engine flames out.
Turbine
The two-stage turbine section consists of a series of turbine
wheels that are used to drive the compressor section and
other components attached to the accessory gearbox. Both
stages may consist of one or more turbine wheels. The first
stage is usually referred to as the gas producer (N1 or NG)
while the second stage is commonly called the power turbine
(N2 or NP). (The letter N is used to denote rotational speed.)
If the first and second stage turbines are mechanically
coupled to each other, the system is said to be a direct-drive
engine or fixed turbine. These engines share a common shaft,
which means the first and second stage turbines, and thus the
compressor and output shaft, are connected. On most turbine
assemblies used in helicopters, the first stage and second
stage turbines are not mechanically connected to each other.
Rather, they are mounted on independent shafts, one inside
the other, and can turn freely with respect to each other. This
is referred to as a “free turbine.”
4-9
The accessory gearbox of the engine houses all of the
necessary gears to drive the numerous components of the
helicopter. Power is provided to the accessory gearbox
through the independent shafts connected to the N1 and
N2 turbine wheels. The N1 stage drives the components
necessary to complete the turbine cycle, making the engine
self-sustaining. Common components driven by the N1
stage are the compressor, oil pump, fuel pump, and starter/
generator. The N2 stage is dedicated to driving the main
rotor and tail rotor drive systems and other accessories such
as generators, alternators, and air conditioning.
Transmission System
The transmission system transfers power from the engine to
the main rotor, tail rotor, and other accessories during normal
flight conditions. The main components of the transmission
system are the main rotor transmission, tail rotor drive
system, clutch, and freewheeling unit. The freewheeling unit
or autorotative clutch allows the main rotor transmission to
drive the tail rotor drive shaft during autorotation. In some
helicopter designs, such as the Bell BH-206, the freewheeling
unit is located in the accessory gearbox. Because it is part
of the transmission system, the transmission lubricates it to
ensure free rotation. Helicopter transmissions are normally
lubricated and cooled with their own oil supply. A sight gauge
is provided to check the oil level. Some transmissions have
chip detectors located in the sump. These detectors are wired
to warning lights located on the pilot’s instrument panel that
illuminate in the event of an internal problem. Some chip
detectors on modern helicopters have a “burn off” capability
and attempt to correct the situation without pilot action. If the
problem cannot be corrected on its own, the pilot must refer
to the emergency procedures for that particular helicopter.
Most helicopters use a dual-needle tachometer or a vertical
scale instrument to show both engine and rotor rpm or a
percentage of engine and rotor rpm. The rotor rpm indicator is
used during clutch engagement to monitor rotor acceleration,
and in autorotation to maintain rpm within prescribed limits.
It is vital to understand that rotor rpm is paramount and that
engine rpm is secondary. If the rotor tachometer fails, rotor
rpm can still be determined indirectly by the engine rpm since
the engine supplies power to the rotor during powered flight.
There have been many accidents where the pilot responded to
the rotor rpm tachometer failure and entered into autorotation
while the engine was still operating.
Look closer at the markings on the gauges in Figure 4-17. All
gauges shown are dual tachometer gauges. The two on the
left have two needles each, one marked with the letter ‘T’
(turbine) the other marked with the letter ‘R’ (rotor). The
lower left gauge shows two arced areas within the same
needle location. In this case, both needles should be nearly
together or superimposed during normal operation. Note the
top left gauge shows two numerical arcs. The outer arc, with
larger numbers, applies one set of values to engine rpm. The
inner arc, or smaller numbers, represents a separate set of
values for rotor rpm. Normal operating limits are shown when
the needles are married or appear superimposed. The top
right gauge shows independent needles, focused toward the
middle of the gauge, with colored limitation areas respective
15
10
1
0
4
30
5
35
ROTOR
R
110
100
90
110
100
90
80
70
60
50
80
70
60
50
40
TURBINE
% RPM
% RPM
120
110
50
105
60
70
100
ROTOR 80
PEEVER
EE
E
TURBINEA
R
90
95
30
100
R
4-10
E
25
3
RPM
R
X
X100
5
40
Main Rotor Transmission
The primary purpose of the main rotor transmission is
to reduce engine output rpm to optimum rotor rpm. This
reduction is different for the various helicopters. As an
example, suppose the engine rpm of a specific helicopter
is 2,700. A rotor speed of 450 rpm would require a 6:1
reduction. A 9:1 reduction would mean the rotor would turn
at 300 rpm.
20
2
T
Accessory Gearbox
Dual Tachometers
R
When the engine is running, the combustion gases pass
through the first stage turbine (N1) to drive the compressor
and other components, and then past the independent
second stage turbine (N2), which turns the power and
accessory gearbox to drive the output shaft, as well as other
miscellaneous components.
20
10
PERCENT
C
RPM
TP
0
110
120
NR
90
80
70
60
40
0
NP
Figure 4-17. Various types of dual-needle tachometers.
to the needle head. The left side represents engine operational
parameters; the right, rotor operational parameters.
Many newer aircraft have what is referred to as a glass
cockpit, meaning the instrumentation is digital and displayed
to the pilot on digital screens and vertical scale instruments.
The bottom right gauge in Figure 4-17 replicates a vertical
scale instrument. The dual tachometer shown displays rotor
rpm (NR) on the left and engine rpm (NP) on the right side
of the vertical scale. Corresponding color limits are present
for each component parameter.
Structural Design
In helicopters with horizontally mounted engines, another
purpose of the main rotor transmission is to change the
axis of rotation from the horizontal axis of the engine to the
vertical axis of the rotor shaft. [Figure 4-18] This is a major
difference in the design of the airplane power plant and power
train whereas the airplane propeller is mounted directly to
the crankshaft or to shaft that is geared to the crankshaft.
Main rotor
Antitorque rotor
Because of the greater weight of a rotor in relation to the
power of the engine, as compared to the weight of a propeller
and the power in an airplane, the rotor must be disconnected
from the engine when the starter is engaged. A clutch allows
the engine to be started and then gradually pick up the load
of the rotor.
Freewheeling turbine engines do not require a separate clutch
since the air coupling between the gas producer turbine and
the power (takeoff) turbine functions as an air clutch for
starting purposes. When the engine is started, there is little
resistance from the power turbine. This enables the gasproducer turbine to accelerate to normal idle speed without
the load of the transmission and rotor system dragging it
down. As the gas pressure increases through the power
turbine, the rotor blades begin to turn, slowly at first and then
gradually accelerate to normal operating rpm.
On reciprocating and single-shaft turbine engines, a clutch
is required to enable engine start. Air, or windmilling starts,
are not possible. The two main types of clutches are the
centrifugal clutch and the idler or manual clutch.
How the clutch engages the main rotor system during engine
start differs between helicopter design. Piston powered
helicopters have a means of engaging the clutch manually
just as a manual clutch in an automobile. This may be by
means of an electric motor that positions a pulley when the
engine is at the proper operating condition (oil temperature
and pressure in the appropriate range), but it is controlled by
a cockpit mounted switch.
Belt Drive Clutch
Main transmission
To engine
Gearbox
Figure 4-18. The main rotor transmission reduces engine output
rpm to optimum rotor rpm.
Some helicopters utilize a belt drive to transmit power from
the engine to the transmission. A belt drive consists of a lower
pulley attached to the engine, an upper pulley attached to the
transmission input shaft, a belt or a set of V-belts, and some
means of applying tension to the belts. The belts fit loosely
over the upper and lower pulley when there is no tension on
the belts. [Figure 4-19]
The importance of main rotor rpm translates directly to lift.
RPM within normal limits produces adequate lift for normal
maneuvering. Therefore, it is imperative not only to know
the location of the tachometers, but also to understand the
information they provide. If rotor rpm is allowed to go below
normal limits, the outcome could be catastrophic.
Some aircraft utilize a clutch for starting. This allows the
engine to be started without requiring power to turn the
transmission. One advantage this concept has is that without
a load on the engine starting may be accomplished with
minimal throttle application. However, caution should also
be used during starting, since rapid or large throttle inputs
may cause overspeeds.
Clutch
In a conventional airplane, the engine and propeller are
permanently connected. However, in a helicopter there is
a different relationship between the engine and the rotor.
Once the engine is running, tension on the belts is gradually
increased. When the rotor and engine tachometer needles are
superimposed, the rotor and the engine are synchronized, and
the clutch is then fully engaged. Advantages of this system
4-11
Fuel Systems
The fuel system in a helicopter is made up of two groups
of components: the fuel supply system and the engine fuel
control system.
Fuel Supply System
The supply system consists of a fuel tank or tanks, fuel quantity
gauges, a shut-off valve, fuel filter, a fuel line to the engine,
and possibly a primer and fuel pumps. [Figure 4-20] The fuel
tanks are usually mounted to the airframe as close as possible
to the CG. This way, as fuel is burned off, there is a negligible
effect on the CG. A drain valve located on the bottom of the
fuel tank allows the pilot to drain water and sediment that may
have collected in the tank. A fuel vent prevents the formation
of a vacuum in the tank, and an overflow drain allows fuel to
expand without rupturing the tank.
Figure 4-19. Idler or manual clutch.
Fuel quantity
Fue
include vibration isolation, simple maintenance, and the
ability to start and warm up the engine without engaging the
rotor. When the clutch is not engaged, engines are very easy
to overspeed, resulting in costly inspections and maintenance.
Power, or throttle control, is very important in this phase of
engine operation.
LOW FUEL LEVEL
WARNING LIGHT
Shut-off valve
Centrifugal Clutch
The centrifugal clutch is made up of an inner assembly and
an outer drum. The inner assembly, which is connected to
the engine driveshaft, consists of shoes lined with material
similar to automotive brake linings. At low engine speeds,
springs hold the shoes in, so there is no contact with the outer
drum, which is attached to the transmission input shaft. As
engine speed increases, centrifugal force causes the clutch
shoes to move outward and begin sliding against the outer
drum. The transmission input shaft begins to rotate, causing
the rotor to turn slowly at first, but increasing as the friction
increases between the clutch shoes and transmission drum.
As rotor speed increases, the rotor tachometer needle shows
an increase by moving toward the engine tachometer needle.
When the two needles are superimposed, the engine and the
rotor are synchronized, indicating the clutch is fully engaged
and there is no further slippage of the clutch shoes.
The turbine engine engages the clutch through centrifugal
force, as stated above. Unless a rotor brake is used to
separate the automatic engagement of the main driveshaft and
subsequently the main rotor, the drive shaft turns at the same
time as the engine and the inner drum of the freewheeling unit
engages gradually to turn the main rotor system.
4-12
FUEL SHOT OFF
k
l tan
Fue
MIX
PULL LEAN
Primer nozzle at cylinder
Primer
Fuel strainer
Throttle
Carburetor
Figure 4-20. A typical gravity feed fuel system, in a helicopter
with a reciprocating engine, contains the components shown here.
The fuel travels from the fuel tank through a shut-off valve,
which provides a means to completely stop fuel flow to the
engine in the event of an emergency or fire. The shut-off
valve remains in the open position for all normal operations.
Most non-gravity feed fuel systems contain both an electric
pump and a mechanical engine driven pump. The electrical
pump is used to maintain positive fuel pressure to the
engine pump and may also serve as a backup in the event of
mechanical pump failure. The electrical pump is controlled
by a switch in the cockpit. The engine driven pump is the
primary pump that supplies fuel to the engine and operates
any time the engine is running. A fuel filter removes moisture
and other sediment from the fuel before it reaches the engine.
These contaminants are usually heavier than fuel and settle to
the bottom of the fuel filter sump where they can be drained
out by the pilot.
Some fuel systems contain a small hand-operated pump
called a primer. A primer allows fuel to be pumped directly
into the intake port of the cylinders prior to engine start. The
primer is useful in cold weather when fuel in the carburetor
is difficult to vaporize.
A fuel quantity gauge located on the pilot’s instrument panel
shows the amount of fuel measured by a sensing unit inside
the tank. Most fuel gauges will indicate in gallons or pounds,
and must be accurate only when empty.
It is worth noting that in accordance with Title 14 of the Code
of Federal Regulations (14 CFR) section 27.1337(b)(1), fuel
quantity indicators “must be calibrated to read ‘zero’ during
level flight when the quantity of fuel remaining in the tank
is equal to the unusable fuel supply.” Therefore, it is of the
utmost importance that the pilot or operator determines an
accurate means of verifying partial or full fuel loads. It is
always a good habit, if possible, to visually verify the fuel on
board prior to flight and determine if adequate fuel is present
for the duration of the flight.
fuel and air to be ignited in the combustion chamber. Refer
to the Pilot’s Handbook of Aeronautical Knowledge for a
detailed explanation and illustration.
Carburetor Ice
The effect of fuel vaporization and decreasing air pressure
in the venturi causes a sharp drop in temperature in the
carburetor. If the air is moist, the water vapor in the air may
condense. Pilots should refer to the FAA-approved Rotorcraft
Flying Manual (RFM) for when and how to apply carburetor
heat. In most cases, the needle should be kept out of the
yellow arc or in the green arc. This is accomplished by using
a carburetor heat system, which eliminates the ice by routing
air across a heat source, such as an exhaust manifold, before it
enters the carburetor. [Figure 4-21] If ice is allowed to form
inside the carburetor, engine failure is a very real possibility
and the ability to restart the engine is greatly reduced.
To carburetor
Filter
Carburetor Heat Off
Additionally, 14 CFR section 27.1305(l)(1) requires newer
helicopters to have warning systems “provide a warning
to the flight crew when approximately 10 minutes of
usable fuel remains in the tank.” Caution should be used
to eliminate unnecessary or erratic maneuvering that could
cause interruption of fuel flow to the engine. Although these
systems must be calibrated, never assume the entire amount
is available. Many pilots have not reached their destinations
due to poor fuel planning or faulty fuel indications.
Engine Fuel Control System
Regardless of the device, the reciprocating engine and the
turbine engine both use the ignition and combustion of the
fuel/air mix to provide the source of their power. Engine
fuel control systems utilize several components to meter
the proper amount of fuel necessary to produce the required
amount of power. The fuel control system in concert with
the air induction components combine the proper amount of
Carburetor heat collector
Manifold pipe is connected to exhaust manifold
Carburetor Heat On
Figure 4-21. When the carburetor heat is turned ON, normal air flow
is blocked, and heated air from an alternate source flows through
the filter to the carburetor.
4-13
Fuel Injection
In a fuel injection system, fuel and air are metered at the fuel
control unit but are not mixed. The fuel is injected directly
into the intake port of the cylinder where it is mixed with
the air just before entering the cylinder. This system ensures
a more even fuel distribution between cylinders and better
vaporization, which in turn promotes more efficient use of
fuel. Also, the fuel injection system eliminates the problem
of carburetor icing and the need for a carburetor heat system.
Electrical Systems
The electrical systems, in most helicopters, reflect the increased
use of sophisticated avionics and other electrical accessories.
More and more operations in today’s flight environment are
dependent on the aircraft’s electrical system; however, all
helicopters can be safely flown without any electrical power
in the event of an electrical malfunction or emergency.
Helicopters have either a 14- or 28-volt, direct-current
electrical system. On small, piston powered helicopters,
electrical energy is supplied by an engine-driven alternator by
means of a belt and pulley system similar to an automobile.
These alternators have advantages over older style generators
as they are lighter in weight, require lower maintenance, and
maintain a uniform electrical output even at low engine rpm.
As a reminder, think of volts or voltage as the measure of
electrical pressure in the system, analogous to pounds per
square inch in water systems. Amperes is the measure of
electrical quantity in the system or available. For example,
a 100-amp alternator would be analogous to a 100 gallon per
hour water pump. [Figure 4-22]
Turbine powered helicopters use a starter/generator system.
The starter/generator is permanently coupled to the accessory
gearbox. When starting the engine, electrical power from the
battery is supplied to the starter/generator, which turns the
engine over. Once the engine is running, the starter/generator
is driven by the engine and is then used as a generator.
Current from the alternator or generator is delivered through a
voltage regulator to a bus bar. The voltage regulator maintains
the constant voltage required by the electrical system by
regulating the output of the alternator or generator. An overvoltage control may be incorporated to prevent excessive
voltage, which may damage the electrical components. The
bus bar serves to distribute the current to the various electrical
components of the helicopter.
A battery is used mainly for starting the engine. In addition,
it permits limited operation of electrical components, such
as radios and lights, without the engine running. The battery
is also a valuable source of standby or emergency electrical
power in the event of alternator or generator failure.
4-14
An ammeter or load meter is used to monitor the electrical
current within the system. The ammeter reflects current
flowing to and from the battery. A charging ammeter
indicates that the battery is being charged. This is normal
after an engine start since the battery power used in starting
is being replaced. After the battery is charged, the ammeter
should stabilize near zero since the alternator or generator is
supplying the electrical needs of the system.
A discharging ammeter means the electrical load is exceeding
the output of the alternator or generator, and the battery
is helping to supply electrical power. This may mean the
alternator or generator is malfunctioning, or the electrical
load is excessive. A load meter displays the load placed on
the alternator or generator by the electrical equipment. The
RFM for a particular helicopter shows the normal load to
expect. Loss of the alternator or generator causes the load
meter to indicate zero.
Electrical switches are used to select electrical components.
Power may be supplied directly to the component or to a
relay, which in turn provides power to the component. Relays
are used when high current and/or heavy electrical cables are
required for a particular component, which may exceed the
capacity of the switch.
Circuit breakers or fuses are used to protect various electrical
components from overload. A circuit breaker pops out when
its respective component is overloaded. The circuit breaker
may be reset by pushing it back in, unless a short or the
overload still exists. In this case, the circuit breaker continues
to pop, indicating an electrical malfunction. A fuse simply
burns out when it is overloaded and needs to be replaced.
Manufacturers usually provide a holder for spare fuses in the
event one has to be replaced in flight. Caution lights on the
instrument panel may be installed to show the malfunction
of an electrical component.
Hydraulics
Most helicopters, other than smaller piston-powered
helicopters, incorporate the use of hydraulic actuators to
overcome high control forces. [Figure 4-23] A typical
hydraulic system consists of actuators, also called servos,
on each flight control, a pump which is usually driven by
the main rotor transmission and a reservoir to store the
hydraulic fluid. Some helicopters have accumulators located
on the pressure side of the hydraulic system. This allows for
a continuous fluid pressure into the system. A switch in the
cockpit can turn the system off, although it is left on under
normal conditions. When the pilot places the hydraulic
switch/circuit breaker into the on position, the electrical
power is being removed from the solenoid valve allowing
hydraulic fluid to enter the system. When the switch/circuit
(Optional Avionics)
Avionics relay
A
V
I
O
N
I
C
S
Avionics master switch
B
U
S
Mag switch
Off
L
R
Both
RET
A
B
V
U
I
S
O
N
B
I
A
C
R
S
Starting vibrator
ADV
L
I
G
H
T
S
L
Left magnetos
Right magnetos
ADV
R
Panel
Position
Beacon
Ammeter
-30
0
+ 60
- 60
Battery switch
+30
AMP
tery
Bat
Starter switch
Trim
Battery relay
Clutch actuator (internal
limit switches shown in
full disengage position)
M/R gearbox
press switch
Starter relay
r
rte
Sta
Release
Hold
B
U
S
B
A
R
Instr
Lndg Lt
Radio
Xpdr
Clutch
Engage
Alternator
Clutch switch
+
F2
F1
Alternator control unit
Alternator switch
Figure 4-22. An electrical system scematic like this sample is included in most POHs. Notice that the various bus bar accessories are
protected by circuit breakers. However, ensure that all electrical equipment is turned off before starting the engine. This protects sensitive
components, particularly the radios, from damage that may be caused by random voltages generated during the starting process.
4-15
Servo actuator,
lateral cyclic
Scupper drain
Pump
Servo actuator,
lateral cyclic
RESERVOIR
Servo actuator,
lateral cyclic
Pressure
Return
Vent
Quick disconnects
Pressure regulator valve
Filter
Solenoid valve
Rotor control
Pilot input
Figure 4-23. A typical hydraulic system for helicopters in the light to medium range.
breaker is put in the off position, the solenoid valve is now
de-energized and closes, which then allows the pilot to
maintain control of the helicopter with the hydraulic fluid in
the actuators. This is known as a failsafe system. If helicopter
electrical power is lost in flight, the pilot is still able to
maintain control of the hydraulic system. A pressure indicator
in the cockpit may also be installed to monitor the system.
When making a control input, the servo is activated and
provides an assisting force to move the respective flight
control, thus reducing the force the pilot must provide. These
boosted flight controls ease pilot workload and fatigue. In
the event of hydraulic system failure, a pilot is still able to
control the helicopter, but the control forces are very heavy.
In those helicopters in which the control forces are so high
that they cannot be moved without hydraulic assistance, two
or more independent hydraulic systems may be installed.
Some helicopters use hydraulic accumulators to store
pressure, which can be used for a short period of time in an
emergency if the hydraulic pump fails. This gives you enough
time to land the helicopter with normal control.
Force Trim
Force trim was a passive system that simply held the cyclic
in a position that gave a control force to transitioning airplane
pilots who had become accustomed to such control forces.
The system uses a magnetic clutch and springs to hold the
cyclic control in the position where it was released. The
system does not use sensor-based data to make corrections,
but rather is used by the pilot to “hold” the cyclic in a desired
position. The most basic versions only applies to the cyclic
requiring the pilot to continue power and tail rotor inputs.
With the force trim on or in use, the pilot can override the
system by disengaging the system through the use of a force
trim release button or, with greater resistance, can physically
manipulate the controls. Some recent basic systems are
referred to as attitude retention systems.
Stability Augmentations Systems
Active Augmentation Systems
Actual systems use electric actuators that provide input to
the hydraulic servos. These servos receive control commands
from a computer that senses external environmental inputs,
such as wind and turbulence. SAS complexity varies by
manufacturer, but can be as sophisticated as providing three
axis stability. That is, computer based inputs adjust attitude,
power and aircraft trim for a more stabilized flight.
Some helicopters incorporate a stability augmentation system
(SAS) to help stabilize the helicopter in flight and in a hover.
The original purpose and design allowed decreased pilot
work load and lessened fatigue. It allowed pilots to place an
aircraft at a set attitude to accomplish other tasks or simply
stabilize the aircraft for long cross-country flights.
Once engaged by the pilot, these systems use a multitude of
sensors from stabilized gyros to electro-mechanical actuators
that provide instantaneous inputs to all flight controls without
pilot assistance. As with any other SAS, it may be overridden
or disconnected by the pilot at any time. Helicopters with
4-16
complex Automatic Flight Control Systems (AFCS) and
autopilots normally have a trim switch referred to as “beeper
trim” or a “coolie hat.” This switch is used when minor
changes to the trim setting are desired.
Stability augmentation systems reduce pilot workload by
improving basic aircraft control harmony and decreasing
disturbances. These systems are very useful when the pilot
is required to perform other duties, such as sling loading and
search-and-rescue operations. Other inputs such as heading,
speed, altitude, and navigation information may be supplied
to the computer to form a complete autopilot system.
Autopilot
Helicopter autopilot systems are similar to stability
augmentation systems, but they have additional features. An
autopilot can actually fly the helicopter and perform certain
functions selected by the pilot. These functions depend on
the type of autopilot and systems installed in the helicopter.
The most common functions are altitude and heading hold.
Some more advanced systems include a vertical speed or
indicated airspeed (IAS) hold mode, where a constant rate
of climb/descent or IAS is maintained by the autopilot. Some
autopilots have navigation capabilities, such as very high
frequency (VHF) OmniRange Navigation System (VOR),
Instrument Landing System (ILS), and global positioning
system (GPS) intercept and tracking, which is especially
useful in instrument flight rules (IFR) conditions. This is
referred to as a coupled system. An additional component,
called a flight director (FD), may also be installed. The FD
provides visual guidance cues to the pilot to fly selected
lateral and vertical modes of operation. The most advanced
autopilots can fly an instrument approach to a hover without
any additional pilot input once the initial functions have
been selected.
The autopilot system consists of electric actuators or servos
connected to the flight controls. The number and location of
these servos depends on the type of system installed. A twoaxis autopilot controls the helicopter in pitch and roll; one
servo controls fore and aft cyclic, and another controls left
and right cyclic. A three-axis autopilot has an additional servo
connected to the antitorque pedals and controls the helicopter
in yaw. A four-axis system uses a fourth servo which controls
the collective. These servos move the respective flight
controls when they receive control commands from a central
computer. This computer receives data input from the flight
instruments for attitude reference and from the navigation
equipment for navigation and tracking reference. An autopilot
has a control panel in the cockpit that allows the pilot to
select the desired functions, as well as engage the autopilot.
For safety purposes, an automatic disengagement feature
is usually included which automatically disconnects the
autopilot in heavy turbulence or when extreme flight attitudes
are reached. Even though all autopilots can be overridden
by the pilot, there is also an autopilot disengagement button
located on the cyclic or collective which allows pilots to
completely disengage the autopilot without removing their
hands from the controls. Because autopilot systems and
installations differ from one helicopter to another, it is very
important to refer to the autopilot operating procedures
located in the RFM.
Environmental Systems
Heating and cooling the helicopter cabin can be accomplished
in different ways. The simplest form of cooling is by ram air.
Air ducts in the front or sides of the helicopter are opened or
closed by the pilot to let ram air into the cabin. This system
is limited as it requires forward airspeed to provide airflow
and also depends on the temperature of the outside air. Air
conditioning provides better cooling but it is more complex
and weighs more than a ram air system.
One of the simplest methods of cooling a helicopter is to
remove the doors allowing air to flow through the cockpit
and engine compartments. Care must be taken to properly
store the doors whether in a designed door holding rack in
a hangar or if it is necessary to carry them in the helicopter.
When storing the doors, care must be taken to not scratch the
windows. Special attention should be paid to ensuring that
all seat belt cushions and any other loose items are stored
away to prevent ingestion into the main or tail rotor. When
reattaching the doors, proper care must be taken to ensure
that they are fully secured and closed.
Air conditioners or heat exchanges can be fitted to the
helicopter as well. They operate by drawing bleed air from
the compressor, passing it through the heart exchanger and
then releasing it into the cabin. As the compressed air is
released, the expansion absorbs heat and cools the cabin. The
disadvantage of this type of system is that power is required
to compress the air or gas for the cooling function, thus
robbing the engine of some of its capability. Some systems
are restricted from use during takeoff and landings.
Piston-powered helicopters use a heat exchanger shroud
around the exhaust manifold to provide cabin heat. Outside
air is piped to the shroud and the hot exhaust manifold heats
the air, which is then blown into the cockpit. This warm air
is heated by the exhaust manifold but is not exhaust gas.
Turbine helicopters use a bleed air system for heat. Bleed air
is hot, compressed, discharge air from the engine compressor.
Hot air is ducted from the compressor to the bleed air heater
4-17
assembly where it is combined with ambient air through
and induction port mounted to the fuselage. The amount of
heat delivered to the helicopter cabin is regulated by a pilotcontrolled bleed air mixing valve.
The pitot tube on a helicopter is very susceptible to ice and
moisture buildup. To prevent this, pitot tubes are usually
equipped with a heating system that uses an electrical element
to heat the tube.
Anti-Icing Systems
Deicing
Deicing is the process of removing frozen contaminant,
snow, ice, and/or slush from a surface. Deicing of the
helicopter fuselage and rotor blades is critical prior to starting.
Helicopters that are unsheltered by hangars are subject
to frost, snow, freezing drizzle, and freezing rain that can
cause icing of rotor blades and fuselages, rendering them
unflyable until cleaned. Asymmetrical shedding of ice from
the blades can lead to component failure, and shedding ice
can be dangerous as it may hit any structures or people that
are around the helicopter. The tail rotor is very vulnerable
to shedding ice damage. Thorough preflight checks should
be made before starting the rotor blades and if any ice was
removed prior to starting, ensure that the flight controls move
freely. While in-flight, helicopters equipped with deicing
systems should be activated immediately after entry into an
icing condition.
Anti-icing is the process of protecting against the formation
of frozen contaminant, snow, ice, or slush on a surface.
Engine Anti-Ice
The anti-icing system found on most turbine-powered
helicopters uses engine bleed air. Bleed air in turbine engines
is compressed air taken from within the engine, after the
compressor stage(s) and before the fuel is injected in the
burners. The bleed air flows through the inlet guide vanes
and to the inlet itself to prevent ice formation on the hollow
vanes. A pilot-controlled, electrically operated valve on the
compressor controls the air flow. Engine anti-ice systems
should be on prior to entry into icing conditions and remain
on until exiting those conditions. Use of the engine anti-ice
system should always be in accordance with the proper RFM.
Carburetor Icing
Carburetor icing can occur during any phase of flight, but is
particularly dangerous when you are using reduced power,
such as during a descent. You may not notice it during the
descent until you try to add power. Indications of carburetor
icing are a decrease in engine rpm or manifold pressure, the
carburetor air temperature gauge indicating a temperature
outside the safe operating range, and engine roughness. Since
changes in rpm or manifold pressure can occur for a number
of reasons, closely check the carburetor air temperature gauge
when in possible carburetor icing conditions. Carburetor air
temperature gauges are marked with a yellow caution arc or
green operating arcs. Refer to the FAA-approved RFM for
the specific procedure as to when and how to apply carburetor
heat. However, in most cases, it is best to keep the needle out
of the yellow arc or in the green arc. This is accomplished
by using a carburetor heat system that eliminates the ice by
routing air across a heat source, such as an exhaust manifold,
before it enters the carburetor.
Airframe Anti-Ice
Airframe and rotor anti-icing may be found on some larger
helicopters, but it is not common due to the complexity,
expense, and weight of such systems. The leading edges of
rotors may be heated with bleed air or electrical elements to
prevent ice formation. Balance and control problems might
arise if ice is allowed to form unevenly on the blades. Research
is being done on lightweight ice-phobic (anti-icing) materials
or coatings. These materials placed in strategic areas could
significantly reduce ice formation and improve performance.
4-18
Chapter Summary
This chapter discussed all of the common components,
sections, and systems of the helicopter. The chapter also
explained how each of them work with one another to make
flight possible.
Chapter 5
Rotorcraft Flight Manual
Introduction
Title 14 of the Code of Federal Regulations (14 CFR) part
91 requires pilot compliance with the operating limitations
specified in approved rotorcraft flight manuals, markings, and
placards. Originally, flight manuals were often characterized
by a lack of essential information and followed whatever
format and content the manufacturer deemed appropriate.
This changed with the acceptance of the General Aviation
Manufacturers Association (GAMA) specification for a
Pilot’s Operating Handbook, which established a standardized
format for all general aviation airplane and rotorcraft flight
manuals. The term “Pilot’s Operating Handbook (POH)” is
often used in place of “Rotorcraft Flight Manual (RFM).”
5-1
However, if “Pilot’s Operating Handbook” is used as the main
title instead of “Rotorcraft Flight Manual,” a statement must
be included on the title page indicating that the document
is the Federal Aviation Administration (FAA) approved
Rotorcraft Flight Manual (RFM). [Figure 5-1]
ROBINSON R22
R OTORCRAFT
F LIGHT
M ANUAL
General Information (Section 1)
The general information section provides the basic descriptive
information on the rotorcraft and the powerplant. In some
manuals there is a three-view drawing of the rotorcraft that
provides the dimensions of various components, including
the overall length and width, and the diameter of the rotor
systems. This is a good place for pilots to quickly familiarize
themselves with the aircraft. Pilots need to be aware of the
dimensions of the helicopter since they often must decide
the suitability of an operations area for themselves, as well
as hanger space, landing pad, and ground handling needs.
Pilots can find definitions, abbreviations, explanations of
symbology, and some of the terminology used in the manual
at the end of this section. At the option of the manufacturer,
metric and other conversion tables may also be included.
Operating Limitations (Section 2)
Figure 5-1. The RFM is a regulatory document in terms of the
maneuvers, procedures, and operating limitations described therein.
Not including the preliminary pages, an FAA-approved
RFM may contain as many as ten sections. These sections
are: General Information; Operating Limitations; Emergency
Procedures; Normal Procedures; Performance; Weight
and Balance; Aircraft and Systems Description; Handling,
Servicing, and Maintenance Supplements; and Safety
and Operational Tips. Manufacturers have the option of
including a tenth section on safety and operational tips and
an alphabetical index at the end of the handbook.
Preliminary Pages
While RFMs may appear similar for the same make and
model of aircraft, each flight manual is unique since it
contains specific information about a particular aircraft,
such as the equipment installed, and weight and balance
information. Therefore, manufacturers are required to include
the serial number and registration on the title page to identify
the aircraft to which the flight manual belongs. If a flight
manual does not indicate a specific aircraft registration and
serial number, it is limited to general study purposes only.
Most manufacturers include a table of contents, which
identifies the order of the entire manual by section number
and title. Usually, each section also contains its own table
of contents. Page numbers reflect the section being read,
1-1, 2-1, 3-1, and so on. If the flight manual is published
in looseleaf form, each section is usually marked with a
divider tab indicating the section number or title, or both.
The emergency procedures section may have a red tab for
quick identification and reference.
5-2
The operating limitations section contains only those
limitations required by regulation or that are necessary for
the safe operation of the rotorcraft, powerplant, systems,
and equipment. It includes operating limitations, instrument
markings, color coding, and basic placards. Some of the
areas included are: airspeed, altitude, rotor, and powerplant
limitations, including fuel and oil requirements; weight and
loading distribution; and flight limitations.
Instrument Markings
Instrument markings may include, but are not limited to,
green, red, and yellow ranges for the safe operation of the
aircraft. The green marking indicates a range of continuous
operation. The red range indicates the maximum or minimum
operation allowed while the yellow range indicates a caution
or transition area.
Airspeed Limitations
Airspeed limitations are shown on the airspeed indicator by
color coding and on placards or graphs in the aircraft. A red
line on the airspeed indicator shows the airspeed limit beyond
which structural damage could occur. This is called the never
exceed speed, or VNE. The normal operating speed range is
depicted by a green arc. A blue line is sometimes added to
show the maximum safe autorotation speed. [Figure 5-2]
Another restriction on maximum airspeed for level flight with
maximum continuous power (VH) may be the availability
of power. An increase in power required due to an increase
in weight, or by G producing maneuvers, may decrease VH.
A decrease in power available caused by increased density
altitude or by weak or faulty engines also decreases VH.
150 0 20
17
12
100
4
AIRSPEED
RS
25
4
30
6
MPH
PH
x 10
0
10
3
2
10
8
1
60
5
5
KNOTS
80
0
T
14
15
40
R
120
20
35
RPM
X100
40
ROTOR
ENGINE
Airspeed-knots
0 to 130 Knots (0 to 150 MPH) continuous operation
130 Knots (150 MPH) maximum
100 Knots (115 MPH) maximum for autorotation
Figure 5-2. Typical airspeed indicator limitations and markings.
Altitude Limitations
If the rotorcraft has a maximum operating density altitude, it
is indicated in this section of the flight manual. Sometimes
the maximum altitude varies based on different gross weights.
Rotor Limitations
Low rotor revolutions per minute (rpm) does not produce
sufficient lift, and high rpm may cause structural damage,
therefore rotor rpm limitations have minimum and maximum
values. A green arc depicts the normal operating range with red
lines showing the minimum and maximum limits. [Figure 5-3]
There are two different rotor rpm limitations: power-on and
power-off. Power-on limitations apply anytime the engine
is turning the rotor and is depicted by a fairly narrow green
band. A yellow arc may be included to show a transition
range, which means that operation within this range is limited
due to the possibility of increased vibrations or harmonics.
This range may be associated with tailboom dynamic modes.
Power-off limitations apply anytime the engine is not turning
the rotor, such as when in an autorotation. In this case, the
green arc is wider than the power-on arc, indicating a larger
operating range.
Powerplant Limitations
The powerplant limitations area describes operating
limitations on the helicopter’s engine including such items
as rpm range, power limitations, operating temperatures,
and fuel and oil requirements. Most turbine engines and
some reciprocating engines have a maximum power and a
maximum continuous power rating. The “maximum power”
Figure 5-3. Markings on a typical dual-needle tachometer in a
reciprocating-engine helicopter. The outer band shows the limits
of the superimposed needles when the engine is turning the rotor.
The inner band indicates the power-off limits.
rating is the maximum power the engine can generate and
is usually limited by time. The maximum power range is
depicted by a yellow arc on the engine power instruments,
with a red line indicating the maximum power that must not
be exceeded. “Maximum continuous power” is the maximum
power the engine can generate continually and is depicted
by a green arc. [Figure 5-4]
60
50
40
70
80
TORQUE
QU
30
20
10
3
90
2
100
1
110
ER
PERCENT
0
120
4
5
TURB
OUT
6
7
TEMP
°C x 100 8
9
Figure 5-4. Torque and turbine outlet temperature (TOT) gauges
are commonly used with turbine-powered aircraft.
The red line on a manifold pressure gauge indicates the
maximum amount of power. A yellow arc on the gauge
warns of pressures approaching the limit of rated power.
[Figure 5-5] A placard near the gauge lists the maximum
readings for specific conditions.
5-3
15
10
5
20
25
MANIFOLD
FOL
S
PRESSURE
IINCHES
OF
F MERCURY
30
35
Press Alt.
Gross
VNE—MPH IAS
(1,000 ft.)
Weight
F OAT
8
4
6
8
10 12 14
0 109 109 105 84 61
--20 109 109 94 72 49
--- More
than
40 109 103 81 59
---60 109 91 70 48
---- 1,700 lb
80 109 80 59
----100 109 70 48
----0 109 109 109 109 98 77
58
20 109 109 109 109 85 67
48
1,700 lb
40 109 109 109 96 75 57
-or less
60 109 109 108 84 66 48
-80 109 109 95 74 57
--100 109 108 84 66 48
--Maximum VNE Doors off—102 MPH IAS
0
NEVER EXCEED SPEED
110
VNE
100
90
-20
80
Figure 5-5. A manifold pressure gauge is commonly used with
piston-powered aircraft.
Weight and Loading Distribution
The weight and loading distribution area contains the
maximum certificated weights, as well as the center of
gravity (CG) range. The location of the reference datum
used in balance computations should also be included in this
section. Weight and balance computations are not provided
here, but rather in the weight and balance section of the
FAA-approved RFM.
Flight Limitations
This area lists any maneuvers which are prohibited, such
as acrobatic flight or flight into known icing conditions. If
the rotorcraft can only be flown in visual flight rules (VFR)
conditions, it is noted in this area. Also included are the
minimum crew requirements, and the pilot seat location, if
applicable, where solo flights must be conducted.
Placards
All rotorcraft generally have one or more placards displayed
that have a direct and important bearing on the safe operation
of the rotorcraft. These placards are located in a conspicuous
place within the cabin and normally appear in the limitations
section. Since VNE changes with altitude, this placard can be
found in all helicopters. [Figure 5-6]
Emergency Procedures (Section 3)
Concise checklists describing the recommended procedures
and airspeeds for coping with various types of emergencies
5-4
KIAS
+4
60
°C
C
0°
0°
70
50
+2
0°
C
C
MAX ALT.
0
2
4
6
8
10
Pressure Altitude (1,000 feet )
12
14
Figure 5-6. Various VNE placards.
or critical situations can be found in this section. Some of
the emergencies covered include: engine failure in a hover
and at altitude, tail rotor failures, fires, and systems failures.
The procedures for restarting an engine and for ditching in
the water might also be included.
Manufacturers may first show the emergencies checklists in
an abbreviated form with the order of items reflecting the
sequence of action. This is followed by amplified checklists
providing additional information to clarify the procedure. To
be prepared for an abnormal or emergency situation, learn
the first steps of each checklist, if not all the steps. If time
permits, refer to the checklist to make sure all items have
been covered. For more information on emergencies, refer
to Chapter 11, Helicopter Emergencies.
Manufacturers are encouraged to include an optional area
titled Abnormal Procedures, which describes recommended
procedures for handling malfunctions that are not considered
to be emergencies. This information would most likely be
found in larger helicopters.
Normal Procedures (Section 4)
Performance (Section 5)
The performance section contains all the information
required by the regulations and any additional performance
information the manufacturer determines may enhance a
pilot’s ability to operate the helicopter safely. Although
the performance section is not in the limitation section and
is therefore not a limitation, operation outside or beyond
the flight tested and documented performance section can
be expensive, slightly hazardous, or outright dangerous
to life and property. If the helicopter is certificated under
14 CFR part 29, then the performance section may very
well be a restrictive limitation. In any event, a pilot should
determine the performance available and plan to stay within
those parameters.
These charts, graphs, and tables vary in style but all
contain the same basic information. Some examples of the
performance information that can be found in most flight
manuals include a calibrated versus indicated airspeed
conversion graph, hovering ceiling versus gross weight
charts, and a height-velocity diagram. [Figure 5-7] For
information on how to use the charts, graphs, and tables,
refer to Chapter 8, Performance.
Weight and Balance (Section 6)
The weight and balance section should contain all the
information required by the FAA that is necessary to calculate
weight and balance. To help compute the proper data, most
manufacturers include sample problems. Weight and balance
is detailed in Chapter 7, Weight and Balance.
Aircraft and Systems Description
(Section 7)
The aircraft and systems description section is an excellent
place to study all the systems found on an aircraft. The
manufacturers should describe the systems in a manner that
is understandable to most pilots. For larger, more complex
12,000
8,000 FT DENSITY ALTITUDE
MIXTURE FULL RICH
10,000
OA
T0
8,000
Pressure Altitude (ft)
The normal procedures section is the section most frequently
used. It usually begins with a listing of airspeeds that
may enhance the safety of normal operations. It is a good
idea to learn the airspeeds that are used for normal flight
operations. The next part of the section includes several
checklists, which cover the preflight inspection, before
starting procedure, how to start the engine, rotor engagement,
ground checks, takeoff, approach, landing, and shutdown.
Some manufacturers also include the procedures for practice
autorotations. To avoid skipping an important step, always
use a checklist when one is available. More information on
maneuvers can be found in Chapter 9, Basic Maneuvers,
and Chapter 10, Advanced Maneuvers.
°F
OA
T2
0°F
OA
6,000
T4
0°F
OA
T6
0°F
OA
4,000
T8
0°F
OA
T1
OA
T1
00
2,000
0
1,400
1,500
°F
20
°F
1,600
1,700
1,800
Gross Weight (lb)
Figure 5-7. One of the performance charts in the performance
section is the In Ground Effect Hover Ceiling versus Gross Weight
chart. This chart can be used to determine how much weight can be
carried and still operate at a specific pressure altitude or, if carrying
a specific weight, what the altitude limitation is.
helicopters, the manufacturer may assume a higher degree of
knowledge. For more information on helicopter systems, refer
to Chapter 5, Helicopter Components, Sections, and Systems.
Handling, Servicing, and Maintenance
(Section 8)
The handling, servicing, and maintenance section describes
the maintenance and inspections recommended by the
manufacturer, as well as those required by the regulations,
and airworthiness directive (AD) compliance procedures.
There are also suggestions on how the pilot/operator can
ensure that the work is done properly.
This section also describes preventative maintenance that
may be accomplished by certificated pilots, as well as the
manufacturer’s recommended ground handling procedures,
including considerations for hangaring, tie down, and general
storage procedures for the helicopter.
5-5
Supplements (Section 9)
Safety and Operational Tips (Section 10)
The supplements section describes pertinent information
necessary to operate optional equipment installed on the
helicopter that would not be installed on a standard aircraft.
Some of this information may be supplied by the aircraft
manufacturer, or by the maker of the optional equipment.
The information is then inserted into the flight manual at the
time the equipment is installed.
The safety and operational tips section is optional and contains
a review of information that could enhance the safety of the
operation. Some examples of the information that might
be covered include: physiological factors, general weather
information, fuel conservation procedures, external load
warnings, low rotor rpm considerations, and recommendations
that if not adhered to could lead to an emergency.
Since civilian manuals are not updated to the extent of
military manuals, the pilot must learn to read the supplements
after determining what equipment is installed and amend
their daily use checklists to integrate the supplemental
instructions and procedures. This is why air carriers must
furnish checklists to their crews. Those checklists furnished
to the crews must incorporate all procedures from any and all
equipment actually installed in the aircraft and the approved
company procedures.
Chapter Summary
5-6
This chapter familiarized the reader with the RFM. It
detailed each section and explained how to follow and better
understand the flight manual to enhance safety of flight.
Chapter 6
Weight and Balance
Introduction
It is vital to comply with weight and balance limits
established for helicopters. Operating above the maximum
weight limitation compromises the structural integrity of
the helicopter and adversely affects performance. Balance
is also critical because, on some fully loaded helicopters,
center of gravity (CG) deviations as small as three inches can
dramatically change a helicopter’s handling characteristics.
Operating a helicopter that is not within the weight and
balance limitations is unsafe. Refer to FAA-H-8083-1,
Aircraft Weight and Balance Handbook, for more detailed
information.
6-1
Weight
When determining if a helicopter is within the weight limits,
consider the weight of the basic helicopter, crew, passengers,
cargo, and fuel. Although the effective weight (load factor)
varies during maneuvering flight, this chapter primarily
considers the weight of the loaded helicopter while at rest.
It is critical to understand that the maximum allowable weight
may change during the flight. When operations include OGE
hovers and confined areas, planning must be done to ensure
that the helicopter is capable of lifting the weight during all
phases of flight. The weight may be acceptable during the
early morning hours, but as the density altitude increases
during the day, the maximum allowable weight may have
to be reduced to keep the helicopter within its capability.
The following terms are used when computing a helicopter’s
weight.
maintain a hover. By adding ballast to the helicopter, the
cyclic position is closer to the CG, which gives a greater
range of control motion in every direction. When operating
at or below the minimum weight of the helicopter, additional
weight also improves autorotational characteristics since
the autorotational descent can be established sooner. In
addition, operating below minimum weight could prevent
achieving the desirable rotor revolutions per minute (rpm)
during autorotations.
Operating above a maximum weight could result in structural
deformation or failure during flight, if encountering excessive
load factors, strong wind gusts, or turbulence. Weight and
maneuvering limitations also are factors considered for
establishing fatigue life of components. Overweight, meaning
overstressed, parts fail sooner than anticipated. Therefore,
premature failure is a major consideration in determination
of fatigue life and life cycles of parts.
Basic Empty Weight
The starting point for weight computations is the basic
empty weight, which is the weight of the standard helicopter,
optional equipment, unusable fuel, and all operating fluids
including engine and transmission oil, and hydraulic fluid
for those aircraft so equipped. Some helicopters might use
the term “licensed empty weight,” which is nearly the same
as basic empty weight, except that it does not include full
engine and transmission oil, just undrainable oil. If flying a
helicopter that lists a licensed empty weight, be sure to add
the weight of the oil to computations.
Although a helicopter is certificated for a specified maximum
gross weight, it is not safe to take off with this load under
some conditions. Anything that adversely affects takeoff,
climb, hovering, and landing performance may require
off-loading of fuel, passengers, or baggage to some weight
less than the published maximum. Factors that can affect
performance include high altitude, high temperature, and high
humidity conditions, which result in a high density altitude.
In-depth performance planning is critical when operating in
these conditions.
Maximum Gross Weight
The maximum weight of the helicopter. Most helicopters
have an internal maximum gross weight, which refers to
the weight within the helicopter structure and an external
maximum gross weight, which refers to the weight of the
helicopter with an external load. The external maximum
weight may vary depending on where it is attached to the
helicopter. Some large cargo helicopters may have several
attachment points for sling load or winch operations. These
helicopters can carry a tremendous amount of weight when
the attachment point is directly under the CG of the aircraft.
Helicopter performance is not only affected by gross weight,
but also by the position of that weight. It is essential to load
the aircraft within the allowable CG range specified in the
RFM’s weight and balance limitations.
Weight Limitations
Weight limitations are necessary to guarantee the structural
integrity of the helicopter and enable pilots to predict
helicopter performance accurately. Although aircraft
manufacturers build in safety factors, a pilot should never
intentionally exceed the load limits for which a helicopter
is certificated. Operating below a minimum weight could
adversely affect the handling characteristics of the helicopter.
During single-pilot operations in some helicopters, a pilot
needs to use a large amount of forward cyclic in order to
6-2
Balance
Center of Gravity
Ideally, a pilot should try to balance a helicopter perfectly so
that the fuselage remains horizontal in hovering flight, with no
cyclic pitch control needed except for wind correction. Since
the fuselage acts as a pendulum suspended from the rotor,
changing the CG changes the angle at which the aircraft hangs
from the rotor. When the CG is directly under the rotor mast,
the helicopter hangs horizontally; if the CG is too far forward
of the mast, the helicopter hangs with its nose tilted down; if
the CG is too far aft of the mast, the nose tilts up. [Figure 6-1]
CG Forward of Forward Limit
A forward CG may occur when a heavy pilot and passenger
take off without baggage or proper ballast located aft of the
rotor mast. This situation becomes worse if the fuel tanks are
located aft of the rotor mast because as fuel burns the CG
continues to shift forward.
CG directly under the rotor mast
CG
Forward CG
Aft CG
CG
CG
Figure 6-1. The location of the CG strongly influences how the helicopter handles.
This condition is easily recognized when coming to a hover
following a vertical takeoff. The helicopter has a nose-low
attitude, and excessive rearward displacement of the cyclic
control is needed to maintain a hover in a no-wind condition.
Do not continue flight in this condition, since a pilot could
rapidly lose rearward cyclic control as fuel is consumed. A
pilot may also find it impossible to decelerate sufficiently to
bring the helicopter to a stop. In the event of engine failure
and the resulting autorotation, there may not be enough cyclic
control to flare properly for the landing.
If flight is continued in this condition, it may be impossible
to fly in the upper allowable airspeed range due to inadequate
forward cyclic authority to maintain a nose-low attitude. In
addition, with an extreme aft CG, gusty or rough air could
accelerate the helicopter to a speed faster than that produced
with full forward cyclic control. In this case, dissymmetry of
lift and blade flapping could cause the rotor disk to tilt aft.
With full forward cyclic control already applied, a pilot might
not be able to lower the rotor disk, resulting in possible loss
of control, or the rotor blades striking the tailboom.
A forward CG is not as obvious when hovering into a strong
wind, since less rearward cyclic displacement is required than
when hovering with no wind. When determining whether a
critical balance condition exists, it is essential to consider the
wind velocity and its relation to the rearward displacement
of the cyclic control.
Lateral Balance
For smaller helicopters, it is generally unnecessary to
determine the lateral CG for normal flight instruction and
passenger flights. This is because helicopter cabins are
relatively narrow and most optional equipment is located
near the centerline. However, some helicopter manuals
specify the seat from which a pilot must conduct solo flight.
In addition, if there is an unusual situation that could affect
the lateral CG, such as a heavy pilot and a full load of fuel
on one side of the helicopter, its position should be checked
against the CG envelope. If carrying external loads in a
position that requires large lateral cyclic control displacement
to maintain level flight, fore and aft cyclic effectiveness could
be limited dramatically. Manufacturers generally account
for known lateral CG displacements by locating external
attachment points opposite the lateral imbalance. Examples
are placement of hoist systems attached to the side, and wing
stores commonly used on military aircraft for external fuel
pods or armament systems.
CG Aft of Aft Limit
Without proper ballast in the cockpit, exceeding the aft CG
may occur when:
•
A lightweight pilot takes off solo with a full load of
fuel located aft of the rotor mast.
•
A lightweight pilot takes off with maximum baggage
allowed in a baggage compartment located aft of the
rotor mast.
•
A lightweight pilot takes off with a combination of
baggage and substantial fuel where both are aft of the
rotor mast.
A pilot can recognize the aft CG condition when coming
to a hover following a vertical takeoff. The helicopter will
have a tail-low attitude, and will need excessive forward
displacement of cyclic control to maintain a hover in a
no-wind condition. If there is a wind, even greater forward
cyclic is needed.
Weight and Balance Calculations
When determining whether a helicopter is properly loaded,
two questions must be answered:
1.
Is the gross weight less than or equal to the maximum
allowable gross weight?
6-3
2.
Is the CG within the allowable CG range, and will
it stay within the allowable range throughout the
duration of flight including all loading configurations
that may be encountered?
To answer the first question, just add the weight of the items
comprising the useful load (pilot, passengers, fuel, oil (if
applicable) cargo, and baggage) to the basic empty weight of
the helicopter. Ensure that the total weight does not exceed
the maximum allowable gross weight.
Reference Datum
Balance is determined by the location of the CG, which
is usually described as a given number of inches from the
reference datum. The horizontal reference datum is an
imaginary vertical plane or point, arbitrarily fixed somewhere
along the longitudinal axis of the helicopter, from which all
horizontal distances are measured for weight and balance
purposes. There is no fixed rule for its location. It may be
located at the rotor mast, the nose of the helicopter, or even
at a point in space ahead of the helicopter. [Figure 6-3]
To answer the second question, use CG or moment
information from loading charts, tables, or graphs in the RFM.
Then using one of the methods described below, calculate
the loaded moment and/or loaded CG and verify that it falls
within the allowable CG range shown in the RFM.
It is important to note that any weight and balance
computation is only as accurate as the information provided.
Therefore, ask passengers what they weigh and add a few
pounds to account for the additional weight of clothing,
especially during the winter months. Baggage should be
weighed on a scale, if practical. If a scale is not available,
compute personal loading values according to each individual
estimate. Figure 6-2 indicates the standard weights for
specific operating fluids. The following terms are used when
computing a helicopter’s balance.
−
Horizontal
datum
+
Aviation Gasoline (AVGAS). . . . . . . . . . . . . . . . . . . . . 6 lb/gal
Jet Fuel (JP-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 lb/gal
Jet Fuel (JP-5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 lb/gal
Reciprocating Engine Oil . . . . . . . . . . . . . . . . . . . . . 7.5 lb/gal*
Turbine Engine Oil. . . . . . . . . . Varies between 6 and 8 lb/gal*
Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.35 lb/gal
* Oil weight is given in pounds per gallon while oil capacity is
usually given in quarts; therefore, convert the amount of oil to
gallons before calculating its weight. Remember, four quarts
equal one gallon.
Figure 6-2. When making weight and balance computations, always
use actual weights if they are available, especially if the helicopter
is loaded near the weight and balance limits.
6-4
Figure 6-3. While the horizontal reference datum can be anywhere
the manufacturer chooses, some manufacturers choose the datum
line at or ahead of the most forward structural point on the
helicopter, in which case all moments are positive. This aids in
simplifying calculations. Other manufacturers choose the datum line
at some point in the middle of the helicopter in which case moments
produced by weight in front of the datum are negative and moments
produced by weight aft of the datum are positive.
The lateral reference datum is usually located at the center
of the helicopter. The location of the reference datum is
established by the manufacturer and is defined in the RFM.
[Figure 6-4]
Front view
Chapter Summary
+
−
This chapter has discussed the importance of computing
the weight and balance of the helicopter. The chapter also
discussed the common terms and meanings associated with
weight and balance.
Lateral datum
Top view
+
−
Figure 6-4. The lateral reference datum is located longitudinally
through the center of the helicopter; therefore, there are positive
and negative values.
6-5
6-6
Chapter 7
Helicopter Performance
Introduction
A pilot’s ability to predict the performance of a helicopter is
extremely important. It helps to determine how much weight
the helicopter can carry before takeoff, if the helicopter
can safely hover at a spe­cific altitude and temperature, the
distance required to climb above obstacles, and what the
maximum climb rate will be.
7-1
Factors Affecting Performance
A helicopter’s performance is dependent on the power output
of the engine and the lift produced by the rotors, whether it is
the main rotor(s) or tail rotor. Any factor that affects engine
and rotor efficiency affects performance. The three major
factors that affect per­formance are density altitude, weight,
and wind. The Pilot’s Handbook of Aeronautical Knowledge,
FAA-H-8083-25, discusses these factors in great detail.
Moisture (Humidity)
Humidity alone is usually not considered an important factor
in calculating density altitude and helicopter performance;
however, it does contribute. There are no rules of thumb used
to compute the effects of humidity on density altitude but
some manufacturers include charts with 80 percent relative
humidity columns as additional information. There appears
to be an approximately 3–4 percent reduction in performance
compared to dry air at the same altitude and temperature,
so expect a decrease in hovering and takeoff performance
in high humidity conditions. Although 3–4 percent seems
insignificant, it can be the cause of a mishap when already
operating at the limits of the helicopter.
Weight
Most performance charts include weight as one of the
variables. By reducing the weight of the helicopter, a pilot
may be able to take off or land safely at a location that
otherwise would be impossible. However, if ever in doubt
about whether a takeoff or landing can be performed safely,
delay your takeoff until more favorable density altitude
conditions exist. If airborne, try to land at a location that has
more favorable conditions, or one where a landing can be
made that does not require a hover.
In addition, at higher gross weights, the increased power
required to hover produces more torque, which means more
antitorque thrust is required. In some heli­copters during high
altitude operations, the maximum antitorque produced by the
tail rotor during a hover may not be sufficient to overcome
torque even if the gross weight is within limits.
Winds
Wind direction and velocity also affect hovering, take­off, and
climb performance. Translational lift occurs any time there is
relative airflow over the rotor disk. This occurs whether the
relative airflow is caused by helicopter movement or by the
wind. As wind speed increases, translational lift increases,
resulting in less power required to hover.
7-2
The wind direction is also an important consideration.
Headwinds are the most desirable as they contribute to the
greatest increase in performance. Strong crosswinds and
tailwinds may require the use of more tail rotor thrust to
maintain directional control. This increased tail rotor thrust
absorbs power from the engine, which means there is less
power available to the main rotor for the production of
lift. Some helicopters even have a critical wind azimuth or
maximum safe relative wind chart. Operating the helicopter
beyond these limits could cause loss of tail rotor effectiveness.
Takeoff and climb performance is greatly affected by wind.
When taking off into a headwind, effective trans­lational lift
is achieved earlier, resulting in more lift and a steeper climb
angle. When taking off with a tailwind, more distance is
required to accelerate through transla­tion lift.
Performance Charts
In developing performance charts, aircraft manufacturers
make certain assumptions about the condition of the
helicopter and the ability of the pilot. It is assumed that the
helicopter is in good operating condition and the engine
is developing its rated power. The pilot is assumed to be
following normal operating procedures and to have average
flying abilities. Average means a pilot capable of doing each
of the required tasks cor­rectly and at the appropriate times.
Using these assumptions, the manufacturer devel­o ps
performance data for the helicopter based on actual flight
tests. However, they do not test the hel­icopter under each
and every condition shown on a performance chart. Instead,
they evaluate specific data and mathematically derive the
remaining data.
Autorotational Performance
Most autorotational performance charts state that autorotational
descent performance is a function of airspeed and is essentially
unaffected by density altitude and gross weight. Keep in mind
that, at some point, the potential energy expended during
the autorotation is converted into kinetic energy for the flare
and touchdown phase of the maneuver. It is at that point
that increased density altitudes and heavier gross weights
have a great impact on the successful completion of the
autorotation. The rotor disk must be able to overcome the
downward momentum of the helicopter and provide enough
lift to cushion the landing. With increased density altitudes
and gross weights, the lift potential is reduced and a higher
collective pitch angle (angle of incidence) is required. The
aerodynamics of autorotation has been presented in detail in
Chapter 3, Aerodynamics of Flight.
Full throttle and 104% rpm
GROSS WEIGHT (KG)
425 450 475 500 525 550 575 600 625
14
12
−1
0°
C
Standard day
0°
C
+1
0°
0f
,60
9
t
ee
A. Pressure Altitude................................8,000 feet
C
12
10
8
A
C
+2
1,370
0°
C
B
7
+3
0°
6
C
+4
0°
C
5
4
2
1
You are to fly a photographer to a remote location to take
pictures of the local wildlife. Using Figure 7-1, can you
safely hover in ground effect at your departure point with
the following conditions?
0°
de
11
3
Sample Hover Problem 1
−2
it u
Pressure altitude (PA x feet in thousands)
13
alt
As density altitude increases, more power is required to
hover. At some point, the power required is equal to the
power available. This establishes the hovering ceiling under
the existing conditions. Any adjustment to the gross weight
by varying fuel, payload, or both, affects the hovering ceiling.
The heavier the gross weight, the lower the hovering ceiling.
As gross weight is decreased, the hover ceiling increases.
IN GROUND EFFECT AT 2-FOOT SKID CLEARANCE
it y
ns
De
Hovering Performance
Helicopter performance revolves around whether or not the
helicopter can be hovered. More power is required during the
hover than in any other flight regime. Obstructions aside, if a
hover can be maintained, a takeoff can be made, especially
with the additional benefit of translational lift. Hover charts
are provided for in ground effect (IGE) hover and out of
ground effect (OGE) hover under various conditions of
gross weight, altitude, temperature, and power. The IGE
hover ceiling is usually higher than the OGE hover ceiling
because of the added lift benefit produced by ground effect.
See Chapter 3, Aerodynamics of Flight, for more details on
IGE and OGE hover. A pilot should always plan an OGE
hover when landing in an area that is uncertain or unverified.
0
900
OAT
°C
°F
−20
−10
0
+10
+20
+30
+40
−4
+14
+32
+50
+68
+86
+104
1,000
C
1,100
1,200
1,300
1,400
GROSS WEIGHT (LB)
IGE hover ceiling vs. gross weight
Figure 7-1. In ground effect hovering ceiling versus gross weight
chart.
B. Temperature..........................................+15 °C
C. Takeoff Gross Weight.........................1,250 lb
RPM..............................................104 percent
First enter the chart at 8,000 feet pressure altitude (point A),
then move right until reaching a point mid­way between the
+10 °C and +20 °C lines (point B). From that point, proceed
down to find the maximum gross weight where a 2 foot
hover can be achieved. In this case, it is approximately 1,280
pounds (point C).
Since the gross weight of your helicopter is less than this,
you can safely hover with these conditions.
7-3
Sample Hover Problem 2
Once you reach the remote location in the previous problem,
you will need to hover OGE for some of the pictures. The
pressure altitude at the remote site is 9,000 feet, and you will
use 50 pounds of fuel getting there. (The new gross weight is
now 1,200 pounds.) The temperature will remain at +15 °C.
Using Figure 7-2, can you accomplish the mission?
OUT OF GROUND EFFECT
Full throttle (or limit manifold pressure) and 104% rpm
GROSS WEIGHT (KG)
425 450 475 500 525 550 575 600 625
14
it u
de
11
B. Outside Air Temperature. . . . . . . . . . . . . . . . . . . 0 °C
0°
C
12
,60
10
ee
t
A
8
C. Gross Weight. . . . . . . . . . . . . . . . . . . . . . . . . 4,250 lb
−1
0f
9
+1
0°
C
−2
C
1
0
900
First, enter the chart at 9,500 feet pressure altitude, then
move right to outside air temperature, 0 °C. From that point,
move down to 4,250 pounds gross weight and then move left
to 5 foot skid height. Drop down to read 66 percent torque
required to hover.
C
+3
0°
C
+4
0°
5
2
C
0°
6
3
D. Desired Skid Height . . . . . . . . . . . . . . . . . . . . . . 5 feet
0°
0°
+2
B
7
4
C
OAT
°C
°F
−20
−10
0
+10
+20
+30
+40
−4
+14
+32
+50
+68
+86
+104
1,000
Climb Performance
Most of the factors affecting hover and takeoff per­formance
also affect climb performance. In addition, turbulent air, pilot
techniques, and overall condition of the helicopter can cause
climb performance to vary.
C
1,100
1,200
1,300
1,400
GROSS WEIGHT (LB)
Max continuous or full throttle
OGE hover ceiling vs. gross weight
Figure 7-2. Out of ground effect hover ceiling versus gross weight
chart.
Enter the chart at 9,000 feet (point A) and proceed to point
B (+15 °C). From there, determine that the maxi­mum gross
weight to hover OGE is approximately 1,130 pounds (point
C). Since your gross weight is higher than this value, you will
not be able to hover in these conditions. To accomplish the
mission, you will need to remove approximately 70 pounds
before you begin the flight.
These two sample problems emphasize the importance of
determining the gross weight and hover ceiling throughout
the entire flight operation. Being able to hover at the take­off
location with a specific gross weight does not ensure the
same performance at the landing point. If the destination
point is at a higher density altitude because of higher
7-4
Sample Hover Problem 3
A. Pressure Altitude . . . . . . . . . . . . . . . . . . . ..9,500 feet
Standard day
alt
Pressure altitude (PA x feet in thousands)
sity
12
For helicopters with dual engines, performance charts provide
torque amounts for both engines.
Using Figure 7-3, determine what torque is required to hover.
Use the following conditions:
n
De
13
elevation, temperature, and/or relative humidity, more power
is required to hover there. You should be able to predict
whether hovering power will be available at the destination
by knowing the temperature and wind conditions, using
the performance charts in the helicopter flight manual, and
making certain power checks during hover and in flight prior
to commencing the approach and landing.
A helicopter flown at the best rate-of-climb speed (VY) obtains
the greatest gain in altitude over a given period of time. This
speed is normally used during the climb after all obstacles
have been cleared and is usu­ally maintained until reaching
cruise altitude. Rate of climb must not be confused with angle
of climb. Angle of climb is a function of altitude gained over
a given distance. The VY results in the highest climb rate, but
not the steepest climb angle, and may not be sufficient to clear
obstructions. The best angle of climb speed (VX) depends upon
the power available. If there is a surplus of power available,
the helicopter can climb vertically, so VX is zero.
Wind direction and speed have an effect on climb
performance, but it is often misunderstood. Airspeed is
the speed at which the helicopter is moving through the
atmosphere and is unaffected by wind. Atmospheric wind
affects only the groundspeed, or speed at which the helicopter
is moving over the Earth’s surface. Thus, the only climb
performance affected by atmospheric wind is the angle of
climb and not the rate of climb.
FA
T
- 6 °C
0
14000
0
0
+4
+6 0
0
B
A
8000
+2
-2
Pressure altitude - feet
10000
0
-4
0
12000
6000
4000
2000
Engine torque - percent
100
90
70
60
50
40 0
Sk
3
5
10
15
50
52
ht
90
00
50
Det mast torque - percent
t
ee
-f
E)
ig
G
he
(O
00
55
100
id
50
80
D
0
475
80
0
450
4250
70
60
50
C
4000
3750
3500
3250
3000
Gross weight - pounds
40
100
90
80
70
60
50
Mast torque - percent
40
-5000
0
5000
10000
15000
Density altitude - feet
Figure 7-3. Torque required for cruise or level flight.
When planning for climb performance, it is first important to
plan for torque settings at level flight. Climb performance charts
show the change in torque, above or below torque, required
for level flight under the same gross weight and atmospheric
conditions to obtain a given rate of climb or descent.
7-5
Sample Cruise or Level Flight Problem
Sample Climb Problem
Determine torque setting for cruise or level flight using
Figure 7-4. Use the following conditions:
Determine climb/descent torque percentage using Figure 7-5.
Use the following conditions:
Pressure Altitude............................................... 8,000 feet
A. Rate of Climb or Descent. . . . . . . . . . . . . . 500 fpm
Outside Air Temperature...................................... +15 °C
B. Maximum Gross Weight . . . . . . . . . . . . . . . . 5,000 lb
A. Indicated Airspeed........................................80 knots
B. Maximum Gross Weight................................5,000 lb
With this chart, first confirm that it is for a pressure altitude
of 8,000 feet with an OAT of 15°. Begin on the left side
at 80 knots indicated airspeed (point A) and move right to
maximum gross weight of 5,000 lb (point B). From that point,
proceed down to the torque reading for level flight, which
is 74 percent torque (point C). This torque setting is used
in the next problem to add or subtract cruise/descent torque
percentage from cruise flight.
With this chart, first locate a 500 fpm rate of climb or descent
(point A), and then move to the right to a maximum gross
weight of 5,000 lb (point B). From that point, proceed down
to the torque percentage, which is 15 percent torque (point C).
For climb or descent, 15 percent torque should be added/
subtracted from the 74 percent torque needed for level flight.
For example, if the numbers were to be used for a climb
torque, the pilot would adjust torque settings to 89 percent
for optimal climb performance.
1,500
PRESSURE ALTITUDE = 8,000 FEET
340 380 420
140
Cont trq avail
130
90
70
80
60
70
Max R/C or Max end
60
Max tro avail
50
30
00
45
00
40
00
35
0
300
20
50
00
50
XMSN LIMIT
40
55
00
GW
(LB
)
30
40
50
60
70
80
90
Legend
Torque (%)
Max range
Max R/C or Max end
Continuous TRQ
Figure 7-4. Maximum rate-of-climb chart.
7-6
100
1,000
900
800
700
600
500
A
400
B
300
40
200
30
100
20
0
10
C
300
0
350
0
40
00
S
45
W
00
EI
50
GH
0
5
0
T
- ( 500
LB
)
100
B
A
True airspeed (knots)
80
110
1,100
OS
120
SO
90
Max range
1,200
Rate of climb or descent (feet per minute)
AF
20
F1
0 10
1,300
280
∆Torque - %
100
Indicated airspeed (knots)
240
10
110
200
GR
fuel flow (pounds per hour)
160
1,400
FAT 15°C
C
0
5
10
15
20
25
30
35
40
Torque (%)
0
Figure 7-5. Climb/descent torque percentage chart.
Chapter Summary
This chapter discussed the factors affecting performance:
density altitude, weight, and wind. Five sample problems
were also given with performance charts to calculate
different flight conditions and determine the performance
of the helicopter.
Chapter 8
Ground Procedures
and Flight
Preparations
Introduction
Once a pilot takes off, it is up to him or her to make sound,
safe decisions throughout the flight. It is equally important for
the pilot to use the same diligence when conducting a preflight
inspection, making maintenance decisions, refueling, and
conducting ground operations. This chapter discusses the
responsibility of the pilot regarding ground safety in and
around the helicopter and when preparing to fly.
8-1
Preflight
Before any flight, ensure the helicopter is airworthy by
inspecting it according to the rotorcraft flight manual (RFM),
pilot’s operating handbook (POH), or other information
supplied either by the operator or the manufacturer.
Remember that it is the responsibility of the pilot in command
(PIC) to ensure the aircraft is in an airworthy condition.
In preparation for flight, the use of a checklist is important
so that no item is overlooked. [Figure 8-1] Follow the
manufacturer’s suggested outline for both the inside and
outside inspection. This ensures that all the items the
manufacturer feels are important are checked. If supplemental
equipment has been added to the helicopter, these procedures
should be included on the checklist as well.
There are two primary methods of deferring maintenance
on rotorcraft operating under part 91. They are the deferral
provision of 14 CFR part 91, section 91.213(d) and an FAAapproved MEL.
The deferral provision of 14 CFR section 91.213(d) is
widely used by most pilot/operators. Its popularity is due
to simplicity and minimal paperwork. When inoperative
equipment is found during preflight or prior to departure, the
decision should be to cancel the flight, obtain maintenance
prior to flight, determine if the flight can be made under the
limitations imposed by the defective equipment, or to defer
the item or equipment.
Maintenance deferrals are not used for in-flight discrepancies.
The manufacturer’s RFM/POH procedures are to be used in
those situations. The discussion that follows is an example of
a pilot who wishes to defer maintenance that would ordinarily
be required prior to flight.
If able to use the deferral provision of 14 CFR section
91.213(d), the pilot determines whether the inoperative
equipment is required by type design or 14 CFR. If the
inoperative item is not required, and the helicopter can be
safely operated without it, the deferral may be made. The
inoperative item shall be deactivated or removed and an
INOPERATIVE placard placed near the appropriate switch,
control, or indicator. If deactivation or removal involves
maintenance (removal always does), it must be accomplished
by certificated maintenance personnel.
Figure 8-1. The pilot in command is responsible for the airworthy
condition of the aircraft and using checklists to ensure proper
inspection of the helicopter prior to flight.
Minimum Equipment Lists (MELs) and Operations
with Inoperative Equipment
Title 14 of the Code of Federal Regulations (14 CFR) requires
that all aircraft instruments and installed equipment be
operative prior to each departure. However, when the Federal
Aviation Administration (FAA) adopted the minimum
equipment list (MEL) concept for 14 CFR part 91 operations,
flights were allowed with inoperative items, as long as the
inoperative items were determined to be nonessential for safe
flight. At the same time, it allowed part 91 operators, without
an MEL, to defer repairs on nonessential equipment within
the guidelines of part 91.
8-2
For example, if the position lights (installed equipment) were
discovered to be inoperative prior to a daytime flight, the pilot
would follow the requirements of 14 CFR section 91.213(d).
The pilot must then decide if the flight can be accomplished
prior to night, when the lights will be needed.
The deactivation may be a process as simple as the pilot
positioning a circuit breaker to the OFF position, or as
complex as rendering instruments or equipment totally
inoperable. Complex maintenance tasks require a certificated
and appropriately rated maintenance person to perform the
deactivation. In all cases, the item or equipment must be
placarded INOPERATIVE.
When an operator requests an MEL, and a Letter of
Authorization (LOA) is issued by the FAA, then the use
of the MEL becomes mandatory for that helicopter. All
maintenance deferrals must be accomplished in accordance
with the terms and conditions of the MEL and the operatorgenerated procedures document.
The use of an MEL for rotorcraft operated under part 91 also
allows for the deferral of inoperative items or equipment. The
primary guidance becomes the FAA-approved MEL issued to
that specific operator and N-numbered helicopter.
The FAA has developed master minimum equipment lists
(MMELs) for rotorcraft in current use. Upon written request
by a rotorcraft operator, the local FAA Flight Standards District
Office (FSDO) may issue the appropriate make and model
MMEL, along with an LOA, and the preamble. The operator
then develops operations and maintenance (O&M) procedures
from the MMEL. This MMEL with O&M procedures now
becomes the operator’s MEL. The MEL, LOA, preamble, and
procedures document developed by the operator must be on
board the helicopter when it is operated.
The FAA considers an approved MEL to be a supplemental
type certificate (STC) issued to an aircraft by serial number
and registration number. It therefore becomes the authority
to operate that aircraft in a condition other than originally
type certificated.
With an approved MEL, if the position lights were discovered
inoperative prior to a daytime flight, the pilot would make
an entry in the maintenance record or discrepancy record
provided for that purpose. The item is then either repaired or
deferred in accordance with the MEL. Upon confirming that
daytime flight with inoperative position lights is acceptable in
accordance with the provisions of the MEL, the pilot would
leave the position lights switch OFF, open the circuit breaker
(or whatever action is called for in the procedures document),
and placard the position light switch as INOPERATIVE.
There are exceptions to the use of the MEL for deferral. For
example, should a component fail that is not listed in the
MEL as deferrable (the rotor tachometer, engine tachometer,
or cyclic trim, for example), then repairs are required to be
performed prior to departure. If maintenance or parts are not
readily available at that location, a special flight permit can
be obtained from the nearest FSDO. This permit allows the
helicopter to be flown to another location for maintenance.
This allows an aircraft that may not currently meet applicable
airworthiness requirements, but is capable of safe flight, to
be operated under the restrictive special terms and conditions
attached to the special flight permit.
Deferral of maintenance is not to be taken lightly, and due
consideration should be given to the effect an inoperative
component may have on the operation of a helicopter,
particularly if other items are inoperative. Further information
regarding MELs and operations with inoperative equipment
can be found in AC 9 1-67, Minimum Equipment Requirements
for General Aviation Operations Under FAR Part 91.
Engine Start And Rotor Engagement
During the engine start, rotor engagement, and systems
ground check, use the manufacturer’s checklists. If a problem
arises, have it checked before continuing. Prior to performing
these tasks, however, make sure the area around and above
the helicopter is clear of personnel and equipment. Position
the rotor blades so that they are not aligned with the fuselage.
This may prevent the engine from being started with the
blades still fastened. For a two bladed rotor system, position
the blades so that they are perpendicular to the fuselage
and easily seen from the cockpit. Helicopters are safe and
efficient flying machines as long as they are operated within
the parameters established by the manufacturer.
Rotor Safety Considerations
The exposed nature of the main and tail rotors deserves
special caution. Exercise extreme care when taxiing near
hangars or obstructions since the distance between the
rotor blade tips and obstructions is very difficult to judge.
[Figure 8-2] In addition, the tail rotor of some helicopters
cannot be seen from the cabin. Therefore, when hovering
backward or turning in those helicopters, allow plenty of
room for tail rotor clearance. It is a good practice to glance
over your shoulder to maintain this clearance.
Figure 8-2. Exercise extreme caution when hovering near buildings
or other aircraft.
Another rotor safety consideration is the thrust a helicopter
generates. The main rotor system is capable of blowing
sand, dust, snow, ice, and water at high velocities for a
significant distance causing injury to nearby people and
damage to buildings, automobiles, and other aircraft. Loose
snow, sand, or soil can severely reduce visibility and obscure
outside visual references. There is also the possibility of
sand and snow being ingested into the engine intake, which
can overwhelm filters and cutoff air to the engine or allow
unfiltered air into the engine, leading to premature failure.
Any airborne debris near the helicopter can be ingested into
the engine air intake or struck by the main and tail rotor
blades.
8-3
Aircraft Servicing
The helicopter rotor blades are usually stopped, and both the
aircraft and the refueling unit properly grounded prior to any
refueling operation. The pilot should ensure that the proper
grade of fuel and the proper additives, when required, are
being dispensed.
Refueling of a turbine aircraft while the blades are turning,
known as “hot refueling,” may be practical for certain types
of operation. However, this can be hazardous if not properly
conducted. Pilots should remain at the flight controls; and
refueling personnel should be knowledgeable about the
proper refueling procedures and properly briefed for specific
helicopter makes and models.
The pilot may need to train the refueling personnel on
proper hot refueling procedures for that specific helicopter.
The pilot should explain communication signs or calls,
normal servicing procedures, and emergency procedures as
a minimum. At all times during the refueling process, the
pilot should remain vigilant and ready to immediately shut
down the engine(s) and egress the aircraft. Several accidents
have occurred due to hot refueling performed by improperly
trained personnel.
Refueling units should be positioned to ensure adequate rotor
blade clearance. Persons not involved with the refueling
operation should keep clear of the area. Smoking must be
prohibited in and around the aircraft during all refueling
operations.
If operations dictate that the pilot must leave the helicopter
during refueling operations, the throttle should be rolled
back to flight idle and flight control friction firmly applied to
prevent uncommanded control movements. The pilot should
be thoroughly trained on setting the controls and egressing/
ingressing the helicopter.
Ramp Attendants and Aircraft Servicing
Personnel
These personnel should be instructed as to their specific
duties and the proper method of fulfilling them. In addition,
the ramp attendant should be taught to:
1.
Keep passengers and unauthorized persons out of the
helicopter landing and takeoff area.
2.
Brief passengers on the best way to approach and
board a helicopter with its rotors turning.
Persons directly involved with boarding or deplaning
passengers, aircraft servicing, rigging, or hooking up external
loads, etc., should be instructed as to their duties. It would be
difficult, if not impossible, to cover each and every type of
operation related to helicopters. A few of the more obvious
and common ones are covered below.
Passengers
All persons boarding a helicopter while its rotors are turning
should be taught the safest means of doing so. The pilot in
command (PIC) should always brief the passengers prior
to engine start to ensure complete understanding of all
procedures. The exact procedures may vary slightly from
one helicopter model to another, but the following should
suffice as a generic guide.
When boarding—
1.
Stay away from the rear of the helicopter.
2.
Approach or leave the helicopter in a crouching
manner.
3.
Approach from the side but never out of the pilot’s line
of vision. Many helicopters have dipping front blades
due to landing gear configuration. For that reason, it
is uniformly accepted for personnel to approach from
the sides of the helicopter. Personnel should always
be cautioned about approaching from the rear due to
the tail rotor hazard, even for helicopters such as the
BO-105 and BK-117.
4.
Carry tools horizontally, below waist level—never
upright or over the shoulder.
5.
Hold firmly onto hats and loose articles.
6.
Never reach up or dart after a hat or other object that
might be blown off or away.
7.
Protect eyes by shielding them with a hand or by
squinting.
8.
If suddenly blinded by dust or a blowing object, stop
and crouch lower; better yet, sit down and wait for
help.
Safety In and Around Helicopters
People have been injured, some fatally, in helicopter accidents
that would not have occurred had they been informed of the
proper method of boarding or deplaning. [Figure 8-3] A
properly briefed passenger should never be endangered by
a spinning rotor. The simplest method of avoiding accidents
of this sort is to stop the rotors before passengers are boarded
or allowed to depart. Because this action is not always
practicable, and to realize the vast and unique capabilities
of the helicopter, it is often necessary to take on passengers
or have them exit the helicopter while the engine and rotors
are turning. To avoid accidents, it is essential that all persons
associated with helicopter operations, including passengers,
be made aware of all possible hazards and instructed how
those hazards can be avoided.
8-4
SAFETY AROUND HELICOPTERS
Approaching or Leaving a Helicopter
Do not approach or leave without the pilot’s visual
acknowledgment. Keep in pilot’s field of vision at all times.
Observe helicopter safety zones (see diagram at right).
PROHIBITED
PROHIBITED
On sloping ground, always approach or leave on the
downslope side for maximum rotor clearance.
ACCEPTABLE
If blinded by swirling dust or grit, STOP—crouch lower,
or sit down and await assistance.
ACCEPTABLE
PREFERRED
If disembarking while helicopter is at the hover, get out and
off in a smooth unhurried manner.
Proceed in a crouching manner for extra rotor clearance.
Hold onto hat unless chin straps are used. NEVER reach
up or chase after a hat or other articles that blow away.
Do not approach or leave a helicopter when the engine and
rotors are running down or starting up.
Carry tools, etc., horizontally below waist level—never upright
or on the shoulder.
Figure 8-3. Safety procedures for approaching or leaving a helicopter.
9.
Never grope or feel your way toward or away from
the helicopter.
10. Protect hearing by wearing earplugs or earmuffs.
Since few helicopters carry cabin attendants, the pilot must
conduct the pretakeoff and prelanding briefings, usually
before takeoff due to noise and cockpit layout. The type
8-5
of operation dictates what sort of briefing is necessary. All
briefings should include the following:
1.
The use and operation of seatbelts for takeoff, en route,
and landing.
2.
For over water flights, the location and use of flotation
gear and other survival equipment that might be on
board. Also include how and when to abandon the
helicopter should ditching become necessary.
3.
For flights over rough or isolated terrain, all occupants
should be told where maps and survival gear are
located.
4.
Passengers should be informed as to what actions and
precautions to take in the event of an emergency, such
as the body position for best spinal protection against
a high vertical impact landing (erect with back firmly
against the seat back); and when and how to exit
after landing. Ensure that passengers are aware of the
location of the fire extinguisher, survival equipment
and, if equipped, how to use and locate the Emergency
Position Indicator Radio Beacon (EPIRB).
5.
Smoking should not be permitted within 50 feet of an
aircraft on the ground. Smoking could be permitted
upwind from any possible fuel fumes, at the discretion
of the pilot, except under the following conditions:
•
During all ground operations.
•
During takeoff or landing.
•
When carrying flammable or hazardous
materials.
When passengers are approaching or leaving a helicopter
that is sitting on a slope with the rotors turning, they should
approach and depart downhill. This affords the greatest
distance between the rotor blades and the ground. If this
involves walking around the helicopter, they should always
go around the front—never the rear.
Pilot at the Flight Controls
Many helicopter operators have been lured into a “quick
turnaround” ground operation to avoid delays at airport
terminals and to minimize stop/start cycles of the engine.
As part of this quick turn-around, the pilot might leave the
cockpit with the engine and rotors turning. Such an operation
can be extremely hazardous if a gust of wind disturbs the
rotor disk, or the collective flight control moves causing
lift to be generated by the rotor system. Either occurrence
may cause the helicopter to roll or pitch, resulting in a rotor
blade striking the tail boom or the ground. Good operating
procedures dictate that, generally, pilots remain at the flight
controls whenever the engine is running and the rotors are
turning.
8-6
If operations require the pilot to leave the cockpit to refuel,
the throttle should be rolled back to flight idle and all
controls firmly frictioned to prevent uncommanded control
movements. The pilot should be well trained on setting
controls and exiting the cockpit without disturbing the flight
or power controls.
After Landing and Securing
When the flight is terminated, park the helicopter where
it does not interfere with other aircraft and is not a hazard
to people during shutdown. For many helicopters, it is
advantageous to land with the wind coming from the right
over the tail boom (counterrotating blades). This tends to
lift the blades over the tail boom, but lowers the blades in
front of the helicopter. This action decreases the likelihood
of a main rotor strike to the tail boom due to gusty winds.
Rotor downwash can cause damage to other aircraft in close
proximity, and spectators may not realize the danger or see
the rotors turning. Passengers should remain in the helicopter
with their seats belts secured until the rotors have stopped
turning. During the shutdown and postflight inspection,
follow the manufacturer’s checklist. Any discrepancies
should be noted and, if necessary, reported to maintenance
personnel.
Chapter Summary
This chapter explained the importance of preflight and safety
when conducting helicopter ground operations. Proper
procedures for engine run-up, refueling, and ground safety
were detailed and the responsibilities of the pilot when
maintenance issues occur before flight.
Chapter 9
Basic
Flight Maneuvers
Introduction
From the previous chapters, it should be apparent that no
two helicopters perform the same way. Even when flying
the same model of helicopter, wind, temperature, humidity,
weight, and equipment make it difficult to predict just how
the helicopter will perform. Therefore, this chapter presents
the basic flight maneuvers in a way that would apply to
the majority of helicopters. In most cases, the techniques
described apply to small training helicopters with:
•
A single, main rotor rotating in a counterclock­wise
direction (looking downward on the rotor).
•
An antitorque system.
9-1
Where a technique differs, it is noted. For example, a power
increase on a helicopter with a clockwise rotor system
requires right antitorque pedal pressure instead of left pedal
pressure. In many cases, the terminology “apply proper pedal
pressure” is used to indicate both types of rotor systems.
However, when discussing throt­tle coordination to maintain
proper rotations per minute (rpm), there is no differentiation
between those helicopters with a gov­ernor and those without.
In a sense, the governor is doing the work for you. In addition,
instead of using the terms “collective pitch control” and
“cyclic pitch control” throughout the chapter, these controls
are referred to as just “collective” and “cyclic.”
Because helicopter performance varies with weather
conditions and aircraft loading, specific nose attitudes and
power settings are not detailed in this handbook. In addition,
this chapter does not detail every attitude of a helicopter in
the various flight maneuvers, nor every move that must be
made in order to perform a given maneuver.
When a maneuver is presented, there is a brief description,
followed by the technique to accomplish the maneuver. In
most cases, there is a list of common errors at the end of the
discussion.
The Four Fundamentals
There are four fundamentals of flight upon which all
maneuvers are based: straight-and-level flight, turns, climbs,
and descents. All controlled flight maneuvers consist of one
or more of the four fundamentals of flight. If a student pilot
is able to perform these maneuvers well, and the student’s
proficiency is based on accurate “feel” and control analysis
rather than mechanical movements, the ability to perform
any assigned maneuver is only a matter of obtaining a clear
visual and mental conception of it. The flight instructor must
impart a good knowledge of these basic elements to the
student, and must combine them and plan their practice so that
perfect performance of each is instinctive without conscious
effort. The importance of this to the success of flight training
cannot be overemphasized. As the student progresses to
more complex maneuvers, discounting any difficulties in
visualizing the maneuvers, most student difficulties are
caused by a lack of training, practice, or understanding of the
principles of one or more of these fundamentals.
Guidelines
Good practices to follow during maneuvering flight include:
1.
9-2
Move the cyclic only as fast as trim, torque, and rotor
can be maintained. When entering a maneuver and the
trim, rotor, or torque reacts quicker than anticipated,
pilot limitations have been exceeded. If continued,
an aircraft limitation will be exceeded. Perform the
maneuver with less intensity until all aspects of the
machine can be controlled. The pilot must be aware
of the sensitivity of the flight controls due to the high
speed of the main rotor.
2.
Anticipate changes in aircraft performance due to
loading or environmental condition. The normal
collective increase to check rotor speed at sea level
standard (SLS) may not be sufficient at 4,000 feet
pressure altitude (PA) and 95 °F.
3.
Anticipate the following characteristics during
aggressive maneuvering flight, and adjust or lead with
collective as necessary to maintain trim and torque:
•
Left turns, torque increases (more antitorque).
This applies to most helicopters, but not all.
•
Right turns, torque decreases (less antitorque).
This applies to most helicopters, but not all.
•
Application of aft cyclic, torque decreases and
rotor speed increases.
•
Application of forward cyclic (especially when
immediately following aft cyclic application),
torque increases and rotor speed decreases.
•
Always leave a way out.
•
Know where the winds are.
•
Engine failures occur during power changes and
cruise flight.
•
Crew coordination is critical. Everyone needs
to be fully aware of what is going on, and each
crewmember has a specific duty.
•
In steep turns, the nose drops. In most cases,
energy (airspeed) must be traded to maintain
altitude as the required excess engine power may
not be available (to maintain airspeed in a 2G/60°
turn, rotor thrust/engine power must increase by
100 percent). Failure to anticipate this at low
altitude endangers the crew and passengers.
The rate of pitch change is proportional to gross
weight and density altitude.
•
Many overtorques during flight occur as the
aircraft unloads from high G maneuvers. This is
due to insufficient collective reduction following
the increase to maintain consistent torque and
rotor rpm as G-loading increased (dive recovery
or recovery from high G-turn to the right).
•
Normal helicopter landings usually require high
power settings, with terminations to a hover
requiring the highest power setting.
•
The cyclic position relative to the horizon
determines the helicopter’s travel and attitude.
Vertical Takeoff to a Hover
A vertical takeoff to a hover involves flying the helicopter
from the ground vertically to a skid height of two to three
feet, while maintaining a constant heading. Once the desired
skid height is achieved, the helicopter should remain nearly
motionless over a reference point at a constant altitude and
on a constant heading. The maneuver requires a high degree
of concentration and coordination.
Technique
The pilot on the controls needs to clear the area left, right,
and above to perform a vertical takeoff to a hover. The
pilot should remain focused outside the aircraft and obtain
clearance to take off from the controlling tower. If necessary,
the pilot who is not on the controls assists in clearing the
aircraft and provides adequate warning of any obstacles and
any unannounced or unusual drift/altitude changes.
Heading control, direction of turn, and rate of turn at hover
are all controlled by using the pedals. Hover height, rate of
ascent, and the rate of descent are controlled by using the
collective. Helicopter position and the direction of travel are
controlled by the cyclic.
After receiving the proper clearance and ensuring that the
area is clear of obstacles and traffic, begin the maneuver
with the collective in the down position and the cyclic in
a neutral position, or slightly into the wind. Very slowly
increase the collective until the helicopter becomes light
on the skids or wheels. At the same time apply pressure
and counter pressure on the pedals to ensure the heading
remains constant. Continue to apply pedals as necessary to
maintain heading and coordinate the cyclic for a vertical
ascent. As the helicopter slowly leaves the ground, check
for proper attitude control response and helicopter center of
gravity. A slow ascent will allow stopping if responses are
outside the normal parameters indicating hung or entangled
landing gear, center of gravity problems, or control issues.
If a roll or tilt begin, decrease the collective and determine
the cause of the roll or tilt. Upon reaching the desired hover
altitude, adjust the flight controls as necessary to maintain
position over the intended hover area. Student pilots should
be reminded that while at a hover, the helicopter is rarely
ever level. Helicopters usually hover left side low due to the
tail rotor thrust being counteracted by the main rotor tilt. A
nose low or high condition is generally caused by loading.
Once stabilized, check the engine instruments and note the
power required to hover.
Excessive movement of any flight control requires a change
in the other flight controls. For example, if the helicopter
drifts to one side while hovering, the pilot naturally moves
the cyclic in the opposite direction. When this is done,
part of the vertical thrust is diverted, resulting in a loss of
altitude. To maintain altitude, increase the collective. This
increases drag on the blades and tends to slow them down. To
counteract the drag and maintain rpm, increase the throttle.
Increased throttle means increased torque, so the pilot must
add more pedal pressure to maintain the heading. This can
easily lead to overcontrolling the helicopter. However, as
level of proficiency increases, prob­lems associated with
overcontrolling decrease. Helicopter controls are usually
more driven by pressure than by gross control movements.
Common Errors
1.
Failing to ascend vertically as the helicopter becomes
airborne.
2.
Pulling excessive collective to become airborne,
causing the helicopter to gain too much altitude.
3.
Overcontrolling the antitorque pedals, which not only
changes the heading of the helicopter, but also changes
the rpm.
4.
Reducing throttle rapidly in situations in which
proper rpm has been exceeded, usually resulting in
exaggerated heading changes and loss of lift, resulting
in loss of altitude.
5.
Failing to ascend slowly.
Hovering
Hovering is a maneuver in which the helicopter is main­tained
in nearly motionless flight over a reference point at a constant
altitude and on a constant heading.
Technique
To maintain a hover over a point, use sideview and peripheral
vision to look for small changes in the helicopter’s attitude
and altitude. When these changes are noted, make the
necessary con­trol inputs before the helicopter starts to
move from the point. To detect small variations in altitude
or position, the main area of visual attention needs to be
some distance from the aircraft, using various points on the
helicopter or the tip-path plane as a reference. Looking too
closely or looking down leads to overcontrolling. Obviously,
in order to remain over a certain point, know where the point
is, but do not focus all attention there.
As with a takeoff, the pilot controls altitude with the collec­
tive and maintains a constant rpm with the throttle. The cyclic
is used to maintain the helicopter’s position; the pedals, to
control heading. To maintain the helicopter in a stabilized
hover, make small, smooth, coordinated corrections. As the
desired effect occurs, remove the correction in order to stop the
helicopter’s movement. For example, if the helicopter begins
to move rearward, apply a small amount of forward cyclic
9-3
pressure. However, neutralize this pres­sure just before the
helicopter comes to a stop, or it will begin to move forward.
After experience is gained, a pilot develops a certain “feel”
for the helicopter. Small deviations can be felt and seen,
so you can make the corrections before the helicopter
actually moves. A certain relaxed looseness develops, and
controlling the helicopter becomes sec­ond nature, rather than
a mechanical response.
Common Errors
1.
Tenseness and slow reactions to movements of the
helicopter.
2.
Failure to allow for lag in cyclic and collective pitch,
which leads to overcontrolling. It is very common for
a student to get ahead of the helicopter. Due to inertia,
it requires some small time period for the helicopter
to respond.
3.
Confusing attitude changes for altitude changes, which
results in improper use of the controls.
4.
Hovering too high, creating a hazardous flight
condition. The height velocity chart should be
referenced to determine the maximum skid height
to hover and safely recover the helicopter should a
malfunction occur.
5.
Hovering too low, resulting in occasional touch­down.
6.
Becoming overly confident over prepared surfaces
when taking off to a hover. Be aware that dynamic
rollover accidents usually occur over a level surface.
Hovering Turn
A hovering turn is a maneuver performed at hovering altitude
in which the nose of the helicopter is rotated either left or
right while maintaining position over a reference point on the
surface. Hovering turns can also be made around the mast or
tail of the aircraft. The maneuver requires the coordination
of all flight controls and demands pre­cise control near the
surface. A pilot should maintain a constant altitude, rate of
turn, and rpm.
Technique
Initiate the turn in either direction by applying anti-torque
pedal pressure toward the desired direction. It should be noted
that during a turn to the left, more power is required because
left pedal pressure increases the pitch angle of the tail rotor,
which, in turn, requires additional power from the engine. A
turn to the right requires less power. (On helicopters with a
clock­wise rotating main rotor, right pedal increases the pitch
angle and, therefore, requires more power.)
9-4
As the turn begins, use the cyclic as necessary (usually into
the wind) to keep the helicopter over the desired spot. To
continue the turn, add more pedal pressure as the helicopter
turns to the cross­wind position. This is because the wind is
striking the tail surface and tail rotor area, making it more
difficult for the tail to turn into the wind. As pedal pressures
increase due to crosswind forces, increase the cyclic pressure
into the wind to maintain position. Use the collective with the
throttle to maintain a constant altitude and rpm. [Figure 9-1]
After the 90° portion of the turn, decrease pedal pressure
slightly to maintain the same rate of turn. Approaching the
180°, or downwind portion, anticipate opposite pedal pressure
due to the tail moving from an upwind position to a down­
wind position. At this point, the rate of turn has a ten­dency
to increase at a rapid rate due to the tendency of the tail
surfaces to weathervane. Because of the tailwind condition,
hold rearward cyclic pressure to keep the helicopter over
the same spot.
The horizontal stabilizer has a tendency to lift the tail during
a tailwind condition. This is the most difficult portion of
the hovering turn. Horizontal and vertical stabilizers have
several different designs and locations, including the canted
stabilizers used on some Hughes and Schweizer helicopters.
The primary purpose of the vertical stabilizer is to unload
the work of the antitorque system and to aid in trimming the
helicopter in flight should the antitorque system fail. The
horizontal stabilizer provides for a more usable CG range
and aids in trimming the helicopter longitudinally.
Because of the helicopter’s tendency to weathervane,
maintaining the same rate of turn from the 180° posi­tion
actually requires some pedal pressure opposite the direction
of turn. If a pilot does not apply opposite pedal pressure,
the helicopter tends to turn at a faster rate. The amount of
pedal pressure and cyclic deflection throughout the turn
depends on the wind velocity. As the turn is finished on the
upwind heading, apply opposite pedal pressure to stop the
turn. Gradually apply forward cyclic pressure to keep the
helicopter from drifting.
Control pressures and direction of application change
continuously throughout the turn. The most dramatic change
is the pedal pressure (and corresponding power requirement)
necessary to control the rate of turn as the helicopter moves
through the downwind portion of the maneuver.
Cyclic—Right
Cyclic—Rearward
Cyclic—Left
Cyclic—Forward
WIND
WIND
Cyclic—Forward
Pedal
Some left in hover, more
left to start turn to left
Pedal
Most left pressure in
turn
Pedal
Changing from left to
right pressure
Pedal
Most right pedal
pressure in turn
Pedal
Some right to stop turn,
then left to maintain
heading
Collective
Adjust collective as
necessary to maintain
proper hover height
Collective
Adjust collective as
necessary to maintain
proper hover height
Collective
Adjust collective as
necessary to maintain
proper hover height
Collective
Adjust collective as
necessary to maintain
proper hover height
Collective
Adjust collective as
necessary to maintain
proper hover height
Throttle
As necessary to
maintain rpm
Throttle
As necessary to
maintain rpm
Throttle
As necessary to
maintain rpm
Throttle
As necessary to
maintain rpm
Throttle
As necessary to
maintain rpm
Normally left pedal
application requires
more throttle
Normally left pedal
application requires
more throttle
Normally left pedal
application requires
more throttle
Normally left pedal
application requires
more throttle
Figure 9-1. Left turns in helicopters with a counterclockwise rotating main rotor are more difficult to execute because the tail rotor
demands more power. This requires you to compensate with additional left pedal and increased throttle. Refer to this graphic throughout
the remainder of the discussion on a hovering turn to the left.
Hovering—Forward Flight
Forward hovering flight is normally used to move a helicopter
to a specific location, and it may begin from a stationary
hover. During the maneuver, constant groundspeed, altitude,
and heading should be maintained.
Technique
Before starting, pick out two references directly in front and
in line with the helicopter. These reference points should be
kept in line throughout the maneuver. [Figure 9-2]
Common Errors
KNOTS
80
70
60
50
100
90
90
10
IN Hg
ALg.
R
30
2 MIN TURN
9 0
30
0
2
29.8
29.9
30.0
3
5 4
I0
5
UP
I
ALT
CALIBRATED
TO
20,000 FEET
6
TEST
15
VERTICAL SPEED
100 FEET PER MINUTE
20
DOWN
5
15
I0
ELEC
33
N
3
30
Failing to use the antitorque pedals properly.
24
8
7
20
W
5.
I0
GS
1
Failing to maintain constant altitude.
I0
I0
E
4.
20
I0
20
STBY PWR
6
Failing to maintain rpm within normal range.
20
50
60
35
FFEET
I00
40
50
60
DC
3.
30
30
40
70
3
5
LOW
RPM
33
Failing to maintain position over the reference point.
20
20
MPH
80
70
L
25
2
MANFOLD
LD
SS
PRESS
120
110
100
80
%RPM
2.
lOW
FUEL
2I
110
100
90
80
70
60
50
20
TR
CHIP
0
R
110
100
90
15
M
STARTER
ON
I5
E
O
I2
Failing to maintain a slow, constant rate of turn.
MR
CHIP
10
1.
Reference point
A
MR
TEMP
CLUTCH
6
Turns can be made in either direction; however, in a high
wind condition, the tail rotor may not be able to produce
enough thrust, which means the pilot cannot control a turn
to the right in a counterclockwise rotor system. Therefore,
if control is ever question­able, first attempt to make a 90°
turn to the left. If sufficient tail rotor thrust exists to turn
the helicopter crosswind in a left turn, a right turn can be
successfully controlled. The opposite applies to helicopters
with clockwise rotor systems. In this case, start the turn to
the right. Hovering turns should be avoided in winds strong
enough to preclude sufficient aft cyclic control to maintain
the helicopter on the selected surface reference point
when headed downwind. Check the flight manual for the
manufacturer’s recom­mendations for this limitation.
Figure 9-2. To maintain a straight ground track, use two reference
points in line and at some distance in front of the helicopter.
9-5
Begin the maneuver from a normal hovering altitude by
applying forward pressure on the cyclic. As movement
begins, return the cyclic toward the neutral position to
maintain low groundspeed—no faster than a brisk walk.
Throughout the maneuver, maintain a constant groundspeed
and path over the ground with the cyclic, a constant heading
with the antitorque pedals, altitude with the collective, and
the proper rpm with the throttle.
To stop the forward movement, apply rearward cyclic
pressure until the helicopter stops. As forward motion stops,
return the cyclic to the neutral position to pre­vent rearward
movement. Forward movement can also be stopped by
simply applying rearward pressure to level the helicopter
and allowing it to drift to a stop.
Reference point
Common Errors
1.
Exaggerated movement of the cyclic, resulting in
erratic movement over the surface.
2.
Failure to use proper antitorque pedal control, resulting
in excessive heading change.
3.
Failure to maintain desired hovering altitude.
4.
Failure to maintain proper rpm.
5.
Failure to maintain alignment with direction of travel.
Hovering—Sideward Flight
Sideward hovering flight may be necessary to move the
helicopter to a specific area when conditions make it
impossible to use forward flight. During the maneu­ver,
a constant groundspeed, altitude, and heading should be
maintained.
Technique
Before starting sideward hovering flight, ensure the area
for the hover is clear, especially at the tail rotor. Constantly
monitor hover height and tail rotor clearance during all
hovering maneuvers to prevent dynamic rollover or tail
rotor strikes to the ground. Then, pick two points of in-line
reference in the direction of sideward hovering flight to help
maintain the proper ground track. These reference points
should be kept in line throughout the maneuver. [Figure 9-3]
Begin the maneuver from a normal hovering altitude by
applying cyclic toward the side in which the movement is
desired. As the movement begins, return the cyclic toward the
neutral position to maintain low groundspeed—no faster than
a brisk walk. Throughout the maneuver, maintain a constant
groundspeed and ground track with cyclic. Maintain heading,
which in this maneuver is perpendicular to the ground track,
with the antitorque pedals, and a constant altitude with the
collective. Use the throttle to maintain the proper operating
9-6
Figure 9-3. The key to hovering sideward is establishing at least
two reference points that help maintain a straight track over the
ground while keeping a constant heading.
rpm. Be aware that the nose tends to weathervane into the
wind. Changes in the pedal position will change the rpm
and must be corrected by collective and/or throttle changes
to maintain altitude.
To stop the sideward movement, apply cyclic pres­sure in
the direction opposite to that of movement and hold it until
the helicopter stops. As motion stops, return the cyclic to
the neutral position to prevent movement in the opposite
direction. Applying sufficient opposite cyclic pressure to
level the helicopter may also stop sideward move­ment. The
helicopter then drifts to a stop.
Common Errors
1.
Exaggerated movement of the cyclic, resulting in
overcontrolling and erratic movement over the surface.
2.
Failure to use proper antitorque pedal control, resulting
in excessive heading change.
3.
Failure to maintain desired hovering altitude.
4.
Failure to maintain proper rpm.
5.
Failure to make sure the area is clear prior to starting
the maneuver.
Hovering—Rearward Flight
Rearward hovering flight may be necessary to move the
helicopter to a specific area when the situation is such that
forward or sideward hovering flight cannot be used. During
the maneuver, maintain a constant groundspeed, altitude, and
heading. Due to the limited visibility behind a helicopter, it
is important that the area behind the helicopter be cleared
before beginning the maneuver. Use of ground personnel is
rec­ommended.
Hover taxi (25 feet or less)
Technique
Before starting rearward hovering flight, pick out two
reference points in front of, and in line with the heli­copter
just like hovering for­ward. [Figure 9-2] The movement of
the helicopter should be such that these points remain in line.
Begin the maneuver from a normal hovering altitude
by applying rearward pressure on the cyclic. After the
movement has begun, position the cyclic to maintain a slow
groundspeed—no faster than a brisk walk. Throughout the
maneuver, maintain constant ground­speed and ground track
with the cyclic, a constant heading with the antitorque pedals,
constant altitude with the collective, and the proper rpm with
the throttle.
To stop the rearward movement, apply forward cyclic and
hold it until the helicopter stops. As the motion stops, return
the cyclic to the neutral position. Also, as in the case of
forward and sideward hovering flight, opposite cyclic can
be used to level the helicopter and let it drift to a stop. Tail
rotor clearance must be maintained. Generally, a higher-thannormal hover altitude is preferred.
Poor surface conditions or skid type helicopters
Figure 9-4. Hover taxi.
Air Taxi
An air taxi is preferred when movements require greater
distances within an airport or heliport bound­ary. [Figure 9-5]
In this case, fly to the new location; however, it is expected
that the helicopter will remain below 100 feet AGL with
an appropriate airspeed and will avoid over flight of other
aircraft, vehicles, and personnel.
Air taxi (100 feet or less)
Common Errors
1.
Exaggerated movement of the cyclic resulting in
overcontrolling and an uneven movement over the
surface.
2.
Failure to use proper antitorque pedal control, resulting
in excessive heading change.
3.
Failure to maintain desired hovering altitude.
4.
Failure to maintain proper rpm.
Technique
5.
Failure to make sure the area is clear prior to starting
the maneuver.
Before starting, determine the appropriate airspeed and
altitude combination to remain out of the cross-hatched or
shaded areas of the height-velocity diagram. Additionally, be
aware of crosswind conditions that could lead to loss of tail
rotor effectiveness. Pick out two references directly in front
of the helicopter for the ground path desired. These reference
points should be kept in line throughout the maneuver.
Taxiing
Taxiing refers to operations on or near the surface of taxiways
or other prescribed routes. Helicopters utilize three different
types of taxiing.
Hover Taxi
A hover taxi is used when operating below 25 feet above
ground level (AGL). [Figure 9-4] Since hover taxi is just like
forward, sideward, or rearward hovering flight, the technique
to perform it is not presented here.
Faster travel
Figure 9-5. Air taxi.
Begin the maneuver from a normal hovering altitude by
applying forward pressure on the cyclic. As move­ment
begins, attain the desired airspeed with the cyclic. Control the
desired altitude with the collective and rpm with the throttle.
Throughout the maneuver, maintain a desired groundspeed
9-7
and ground track with the cyclic, a constant heading with
antitorque pedals, the desired altitude with the collective,
and proper operating rpm with the throttle.
To stop the forward movement, apply aft cyclic pressure to
reduce forward speed. Simultaneously lower the col­lective to
initiate a descent to hover altitude. As forward motion stops,
return the cyclic to the neutral posi­tion to prevent rearward
movement. As approaching the proper hover altitude,
increase the collective as necessary to stop descent at hover
altitude (much like a quick stop maneuver).
Common Errors
1.
Erratic movement of the cyclic, resulting in improper
airspeed control and erratic movement over the surface.
2.
Failure to use proper antitorque pedal control, result­ing
in excessive heading change.
3.
Failure to maintain desired altitude.
4.
Failure to maintain proper rpm.
5.
Overflying parked aircraft causing possible dam­age
from rotor downwash.
6.
Flying in the cross-hatched or shaded area of the
height-velocity diagram.
7.
Flying in a crosswind that could lead to loss of tail
rotor effectiveness.
8.
Excessive tail-low attitudes.
9.
Excessive power used or required to stop.
10. Failure to maintain alignment with direction of travel.
Surface Taxi
A surface taxi is used to minimize the effects of rotor
downwash. [Figure 9-6] Avoid excessive cyclic displacement
while surface taxiing or on the ground which can lead to main
rotor blades contacting the helicopter or rotor mast. This
technique may be used with wheeled aircraft, or with those
that have floats, skids or skis.
Surface taxi
Less rotor downwash
Figure 9-6. Surface taxi.
9-8
Technique
The helicopter should be in a stationary position on the surface
with the collective full down and the rpm the same as that
used for a hover. This rpm should be maintained throughout
the maneuver. Then, move the cyclic slightly forward and
apply gradual upward pres­sure on the collective to move
the helicopter forward along the surface. Use the antitorque
pedals to maintain heading and the cyclic to maintain ground
track. The collective controls starting, stopping, and speed
while taxiing. The higher the collective pitch, the faster the
taxi speed; however, do not taxi faster than a brisk walk. If
the helicopter is equipped with brakes, use them to help slow
down. Do not use the cyclic to control groundspeed.
During a crosswind taxi, hold the cyclic into the wind a
sufficient amount to eliminate any drifting movement.
Common Errors
1.
Improper use of cyclic.
2.
Failure to use antitorque pedals for heading control.
3.
Improper use of the controls during crosswind
operations.
4.
Failure to maintain proper rpm.
Normal Takeoff From a Hover
A normal takeoff from a hover is an orderly transition to
forward flight and is executed to increase altitude safely and
expeditiously. During the takeoff, fly a pro­file that avoids the
cross-hatched or shaded areas of the height-velocity diagram.
Technique
Refer to Figure 9-7 (position 1). Bring the helicopter to a
hover and make a performance check, which includes power,
balance, and flight controls. The power check should include
an evaluation of the amount of excess power available; that
is, the difference between the power being used to hover and
the power available at the existing altitude and temperature
conditions. The balance condition of the helicopter is
indicated by the position of the cyclic when maintaining a
stationary hover. Wind necessitates some cyclic deflection,
but there should not be an extreme deviation from neutral.
Flight controls must move freely, and the hel­icopter should
respond normally. Then, visually clear the surrounding area.
Start the helicopter moving by smoothly and slowly eas­ing the
cyclic forward (position 2). As the helicopter starts to move
forward, increase the collective, as nec­essary, to prevent the
helicopter from sinking and adjust the throttle to maintain
rpm. The increase in power requires an increase in the proper
antitorque pedal to maintain heading. Maintain a straight
takeoff path throughout the takeoff.
5
4
3
1
2
Figure 9-7. The helicopter takes several positions during a normal takeoff from hover.
While accelerating through effec­tive translational lift (position
3), the helicopter begins to climb and the nose tends to rise
due to increased lift. At this point, adjust the collective to
obtain normal climb power and apply enough forward cyclic
to overcome the tendency of the nose to rise. At position 4,
hold an attitude that allows a smooth acceleration toward
climb­ing airspeed and a commensurate gain in altitude so that
the takeoff profile does not take the helicopter through any
of the cross-hatched or shaded areas of the height-velocity
diagram. As airspeed increases (position 5), place the aircraft
in trim and allow a crab to take place to maintain ground track
and a more favorable climb configuration. As the helicopter
continues to climb and accel­erate to best rate-of-climb, apply
aft cyclic pressure to raise the nose smoothly to the normal
climb attitude.
Normal Takeoff From the Surface
Normal takeoff from the surface is used to move the helicopter
from a position on the surface into effective translational lift
and a normal climb using a minimum amount of power. If the
surface is dusty or covered with loose snow, this technique
provides the most favorable visibility conditions and reduces
the possibility of debris being ingested by the engine.
1.
Failing to use sufficient collective pitch to pre­vent loss
of altitude prior to attaining transla­tional lift.
2.
Adding power too rapidly at the beginning of the
transition from hovering to forward flight without
forward cyclic compensation, causing the helicopter
to gain excessive altitude before acquiring airspeed.
3.
Assuming an extreme nose-down attitude near the
surface in the transition from hovering to forward
flight.
Technique
Place the helicopter in a stationary position on the sur­face.
Lower the collective to the full down position, and reduce
the rpm below operating rpm. Visually clear the area and
select terrain features or other objects to aid in maintaining
the desired track during takeoff and climb out. Increase the
throttle to the proper rpm, and raise the collective slowly
until the helicopter is light on the skids. Hesitate momentarily
and adjust the cyclic and antitorque pedals, as neces­sary, to
prevent any surface movement. Continue to apply upward
collective. As the helicopter leaves the ground, use the cyclic,
as necessary, to begin forward movement as altitude is
gained. Continue to acceler­ate, and as effective translational
lift is attained, the helicopter begins to climb. Adjust attitude
and power, if necessary, to climb in the same manner as a
takeoff from a hover. A second less efficient but acceptable
technique is to attempt a vertical takeoff to evaluate if power
or lift is sufficient to clear obstructions. This allows the
helicopter to be returned to the takeoff position if required.
4.
Failing to maintain a straight flightpath over the
surface (ground track).
Common Errors
Common Errors
5.
Failing to maintain proper airspeed during the climb.
6.
Failing to adjust the throttle to maintain proper rpm.
7.
Failing to transition to a level crab to maintain ground
track.
1.
Departing the surface in an attitude that is too noselow. This situation requires the use of exces­sive power
to initiate a climb.
9-9
Ground Track
Application of the collective that is too abrupt when
departing the surface, causing rpm and heading control
errors.
d
Hea
3.
p te r
Using excessive power combined with a level attitude,
which causes a vertical climb, unless needed for
obstructions and landing considerations.
co
Heli
2.
in g
Crosswind Considerations During
Takeoffs
Wind Movement
If the takeoff is made during crosswind conditions, the
helicopter is flown in a slip during the early stages of the
maneuver. [Figure 9-8] The cyclic is held into the wind a
sufficient amount to maintain the desired ground track for
the takeoff. The heading is maintained with the use of the
antitorque pedals. In other words, the rotor is tilted into the
wind so that the sideward movement of the helicopter is
just enough to counter­act the crosswind effect. To prevent
the nose from turning in the direction of the rotor tilt, it is
necessary to increase the antitorque pedal pressure on the
side opposite the cyclic.
Figure 9-9. To compensate for wind drift at altitude, crab the
helicopter into the wind.
Helicopter
side movement
Wind movement
Figure 9-8. During a slip, the rotor disk is tilted into the wind.
component from the main rotor. By doing this, it causes the
nose of the helicopter to lower which in turn will cause the
airspeed to increase. In order to counteract this, the pilot
must find the correct power setting to maintain level flight
by adjusting the collective. [Figure 9-10] The horizontal
stabilizer aids in trimming the helicopter longitudinally and
reduces the amount of nose tuck that would occur. On several
helicopters, it is designed as a negative lift airfoil, which
produces a lifting force in a downward direction.
After approximately 50 feet of altitude is gained, make a
coordinated turn into the wind to maintain the desired ground
track. This is called crabbing into the wind. The stronger
the crosswind, the more the helicopter has to be turned into
the wind to maintain the desired ground track. [Figure 9-9]
A
MR
TEMP
CLUTCH
90
80
TR
CHIP
lOW
FUEL
LOW
RPM
70
60
20
I0
I0
I0
I0
20
STBY PWR
R
24
8
7
20
35
2 MIN TURN
DC
9 0
30
2
29.8
29.9
30.0
3
5 4
I0
5
UP
0
I
ALT
CALIBRATED
TO
20,000 FEET
6
TEST
2I
30
FFEET
I00
20
50
60
80
70
I5
5
M
STARTER
ON
40
50
L
25
2
MANFOLD
LD
SS
PRESS
IN Hg
ALg.
O
30
30
40
I2
10
20
20
MPH
15
VERTICAL SPEED
100 FEET PER MINUTE
20
DOWN
5
6
%RPM
20
120
110
100
15
I0
ELEC
N
3
GS
E
W
30
33
6
1
9-10
100
90
3
Technique
To maintain forward flight, the rotor tip-path plane must
be tilted forward to obtain the necessary horizontal thrust
80
70
60
50
33
Straight-and-level flight is flight in which constant altitude
and heading are maintained. The attitude of the rotor disk
relative to the horizon determines the airspeed. The horizontal
stabilizer design determines the helicopter’s attitude when
stabilized at an airspeed and altitude. Altitude is primarily
controlled by use of the collective.
KNOTS
110
100
90
80
70
60
50
15
MR
CHIP
0
R
10
Straight-and-Level Flight
E
110
100
90
Figure 9-10. Maintain straight-and-level flight by adjusting the rotor
tip-path plane forward but adjusting the collective as necessary to
maintain a constant airspeed and altitude. The natural horizon line
can be used as an aid in maintaining straight-and-level flight. If
the horizon line begins to rise, slight power may be required or the
nose of the helicopter may be too low. If the horizon line is slowly
dropping, some power may need to be taken out or the nose of the
helicopter may be too high, requiring a cyclic adjustment.
When in straight-and-level flight, any increase in the collective,
while holding airspeed constant, causes the helicopter to climb.
A decrease in the collective, while holding airspeed constant,
causes the helicopter to descend. A change in the collective
requires a coordi­nated change of the throttle to maintain a
constant rpm. Additionally, the antitorque pedals need to keep
the helicopter in trim around the vertical axis.
To increase airspeed in straight-and-level flight, apply
forward pressure on the cyclic and raise the collective as
necessary to maintain altitude. To decrease airspeed, apply
rearward pressure on the cyclic and lower the collective, as
necessary, to maintain altitude.
Although the cyclic is sensitive, there is a slight delay in
control reaction, and it is necessary to antici­pate actual
movement of the helicopter. When making cyclic inputs to
control the altitude or airspeed of a hel­icopter, take care not
to overcontrol. If the nose of the helicopter rises above the
level-flight attitude, apply forward pressure to the cyclic to
bring the nose down. If this correction is held too long, the
nose drops too low. Since the helicopter continues to change
attitude momentarily after the controls reach neutral, return
the cyclic to neutral slightly before the desired attitude is
reached. This principle holds true for any cyclic input.
Since helicopters are not very stable, but are inherently very
controllable, if a gust or turbulence causes the nose to drop,
the nose tends to continue to drop instead of returning to a
straight-and-level attitude as it would on a fixed-wing aircraft.
Therefore, a pilot must remain alert and fly the helicop­ter
at all times.
Common Errors
1.
Failure to trim the helicopter properly, tending to hold
antitorque pedal pressure and opposite cyclic. This is
commonly called cross-controlling.
2.
Failure to maintain desired airspeed.
3.
Failure to hold proper control position to main­tain
desired ground track.
4.
Failure to allow helicopter to stabilize at new airspeed.
Turns
A turn is a maneuver used to change the heading of the
helicopter. The aerodynamics of a turn were previously
discussed in Chapter 3, Aerodynamics of Flight.
Technique
Before beginning any turn, the area in the direction of the
turn must be cleared not only at the helicopter’s alti­tude, but
also above and below. To enter a turn from straight-and-level
flight, apply sideward pressure on the cyclic in the direction
the turn is to be made. This is the only control movement
needed to start the turn. Do not use the pedals to assist the
turn. Use the pedals only to compensate for torque to keep
the helicopter in trim around the vertical axis. [Figure 9-11]
Keeping the fuselage in the correct streamlined position
around the vertical axis facilitates the helicopter flying
forward with the least drag. Trim is indicated by a yaw string
in the center, or a centered ball on a turn and slip indicator.
Inertia
HCL
Figure 9-11. During a level, coordinated turn, the rate of turn
is commensurate with the angle of bank used, and inertia and
horizontal component of lift (HCL) are equal.
How fast the helicopter banks depends on how much lateral
cyclic pressure is applied. How far the helicop­ter banks (the
steepness of the bank) depends on how long the cyclic is
displaced. After establishing the proper bank angle, return
the cyclic toward the neutral position. When the bank is
established, returning the cyclic to neutral or holding it
inclined relative to the horizon will maintain the helicopter
at that bank angle. Increase the collective and throttle to
maintain altitude and rpm. As the torque increases, increase
the proper antitorque pedal pressure to maintain longi­tudinal
trim. Depending on the degree of bank, addi­tional forward
cyclic pressure may be required to maintain airspeed.
Rolling out of the turn to straight-and-level flight is the same
as the entry into the turn except that pressure on the cyclic
is applied in the opposite direction. Since the helicopter
continues to turn as long as there is any bank, start the rollout
before reaching the desired heading.
The discussion on level turns is equally applicable to making
turns while climbing or descending. The only difference is
that the helicopter is in a climbing or descending attitude
rather than that of level flight. If a simultaneous entry is
desired, merely combine the techniques of both maneuvers—
climb or descent entry and turn entry. When recovering
from a climbing or descending turn, the desired heading and
altitude are rarely reached at the same time. If the heading is
9-11
reached first, stop the turn and maintain the climb or descent
until reaching the desired altitude. On the other hand, if the
altitude is reached first, establish the level flight attitude and
continue the turn to the desired heading.
Slips
A slip occurs when the helicopter slides sideways toward
the center of the turn. [Figure 9-12] It is caused by an
insufficient amount of antitorque pedal in the direction of
the turn, or too much in the direction oppo­site the turn, in
relation to the amount of power used. In other words, if you
hold improper antitorque pedal pres­sure, which keeps the
nose from following the turn, the helicopter slips sideways
toward the center of the turn.
Skid
HCL
Inertia
Figure 9-13. During a skid, the rate of turn is too great for the
angle of bank used, and inertia exceeds the horizontal component
of lift (HCL).
Slip
Slip
HCL
0
2
SA
2
50
-4
4
6
8
knots
8
6
H
NET
ALT
8
VOL BATT
PWR
KNOTS
−
7
SEL
PUS
6
FOR
N
30
60
E
120
150
300
330
STEE
STEER
EER
I
ALT
2
29.8
9
2
29.9
29
30.0
3
5 4
FOR
S
210 240
W
STEE
STEER
EER
ON
ON
RADIO
Coordinated
0
4
6
8
knots
8
6
120
NET
knots
80
100
20
0
70
GO
FEET
F
I00
9 0
FNCN
AVG
+
L
NAV
PULL
160
140
10
60
H
OFF
60
40
10
winter
4
90
2
2
-4
PUS
ALT
8
VOL BATT
PWR
DIST
PUSH
O
LT
0
10
-2
80
SA
kno
ts
Acceleration
8
G UNITS
10
6
4
2
0
50
KNOTS
−
HW
7
SEL
PUS
6
FOR
N
30
60
E
120
150
300
330
STEE
STEER
EER
I
ALT
CALIBRATED
TO
20,000 FEET
2
29.8
9
2
29.9
29
30.0
3
5 4
H
FOR
S
210 240
W
STEE
STEER
EER
ON
ON
RADIO
Skid
0
6
8
8
6
NET
FNCN
AVG
+
DIST
ALT
knots
120
80
100
20
0
I00
L
NAV
PULL
160
140
10
70
GO
OFF
60
40
10
knots
winter
4
90
4
60
H
HW
2
2
-4
PUS
PUSH
O
LT
0
10
-2
80
SA
kno
ts
Acceleration
8
G UNITS
10
6
4
2
0
50
In summary, a skid occurs when the rate of turn is too great
for the amount of bank being used, and a slip occurs when
the rate of turn is too low for the amount of bank being used.
[Figure 9-14]
FEET
F
CALIBRATED
TO
20,000 FEET
H
Skids
A skid occurs when the helicopter slides sideways away from
the center of the turn. [Figure 9-13] It is caused by too much
antitorque pedal pressure in the direction of the turn, or by
too little in the direction opposite the turn in relation to the
amount of power used. If the helicopter is forced to turn faster
with increased pedal pressure instead of by increasing the
degree of the bank, it skids sideways away from the center
of the turn instead of flying in its normal curved path.
80
100
9 0
FNCN
+
L
NAV
DIST
HW
Figure 9-12. During a slip, the rate of turn is too low for the angle
of bank used, and the horizontal component of lift (HCL) exceeds
inertia.
knots
120
20
0
I00
AVG
PULL
160
140
10
70
GO
OFF
60
40
10
winter
4
60
PUS
PUSH
O
LT
0
10
-2
90
kno
ts
Acceleration
8
G UNITS
80
6
4
2
0
10
Inertia
KNOTS
8
VOL BATT
PWR
−
7
SEL
PUS
H
FEET
F
9 0
CALIBRATED
TO
20,000 FEET
6
FOR
N
I
ALT
5 4
30
60
E
120
150
300
330
STEE
STEER
EER
2
29.8
9
2
29.9
29
30.0
3
FOR
S
210 240
W
STEE
STEER
EER
ON
ON
RADIO
Figure 9-14. Cockpit view of a slip and skid.
9-12
Normal Climb
Normal Descent
The entry into a climb from a hover has already been described
in the Normal Takeoff from a Hover subsection; there­fore,
this discussion is limited to a climb entry from cruising flight.
A normal descent is a maneuver in which the helicop­ter loses
altitude at a controlled rate in a controlled attitude.
Technique
To enter a climb in a helicopter while maintaining airspeed,
the first actions are increasing the collective and throttle,
and adjusting the pedals as necessary to maintain a centered
ball in the slip/skid indicator. Moving the collective up
requires a slight aft movement of the cyclic to direct all
of the increased power into lift and maintain the airspeed.
Remember, a helicopter can climb with the nose down and
descend with the nose up. Helicopter attitude changes mainly
reflect acceleration or deceleration, not climb or descent.
Therefore, the climb attitude is approximately the same as
level flight in a stable climb, depending on the aircraft’s
horizontal stabilizer design.
If the pilot wishes to climb faster, with a decreased airspeed,
then the climb can be initiated with aft cyclic. Depending
on initial or entry airspeed for the climb, the climb can be
accomplished without increasing the collective, if a much
slower airspeed is acceptable. However, as the airspeed
decreases, the airflow over the vertical fin decreases
necessitating more antitorque (left) pedal application.
To level off from a climb, start adjusting the attitude to the
level flight attitude a few feet prior to reaching the desired
altitude. The amount of lead depends on the rate of climb at
the time of level-off (the higher the rate of climb, the more
the lead). Generally, the lead is 10 percent of the climb rate.
For example, if the climb rate is 500 feet per minute (fpm),
you should lead the level-off by 50 feet.
To begin the level-off, apply forward cyclic to adjust and
maintain a level flight attitude, which can be slightly nose
low. Maintain climb power until the airspeed approaches the
desired cruising airspeed, then lower the collective to obtain
cruising power and adjust the throttle to obtain and maintain
cruising rpm. Throughout the level-off, maintain longitudinal
trim with the antitorque pedals.
Common Errors
1.
Failure to maintain proper power and airspeed.
2.
Holding too much or too little antitorque pedal.
3.
In the level-off, decreasing power before adjusting the
nose to cruising attitude.
Technique
To establish a normal descent from straight-and-level flight
at cruising airspeed, lower the collective to obtain proper
power, adjust the throttle to maintain rpm, and increase
right antitorque pedal pressure to maintain heading in a
counterclockwise rotor system, or left pedal pressure in
a clockwise system. If cruising airspeed is the same as or
slightly above descending air­speed, simultaneously apply
the necessary cyclic pressure to obtain the approximate
descending attitude. If the pilot wants to decelerate, the
cyclic must be moved aft. If the pilot desires to descend
with increased airspeed, then forward cyclic is all that is
required if airspeed remains under the limit. As the helicopter
stabilizes at any forward airspeed, the fuselage attitude will
streamline due to the airflow over the horizontal stabilizer. As
the airspeed changes, the airflow over the vertical stabilizer
or fin changes, so the pedals must be adjusted for trim.
The pilot should always remember that the total lift and thrust
vectoring is controlled by the cyclic. If a certain airspeed
is desired, it will require a certain amount of cyclic and
collective movement for level flight. If the cyclic is moved,
the thrust-versus-lift ration is changed. Aft cyclic directs
more power to lift, and altitude increases. Forward cyclic
directs more power to thrust, and airspeed increases. If the
collective is not changed and there is a change only in cyclic,
the total thrust to lift ration does not change; aft cyclic results
in a climb, and forward cyclic results in a descent with the
corresponding airspeed changes.
To level off from the descent, lead the desired altitude by
approximately 10 percent of the rate of descent. For exam­ple,
a 500 fpm rate of descent would require a 50 foot lead. At
this point, increase the collective to obtain cruising power,
adjust the throttle to maintain rpm, and increase left antitorque
pedal pressure to maintain heading (right pedal pressure in a
clockwise rotor system). Adjust the cyclic to obtain cruising
airspeed and a level flight atti­tude as the desired altitude is
reached.
Common Errors
1.
Failure to maintain constant angle of decent dur­ing
training.
9-13
2.
Failure to level-off the aircraft sufficiently, which
results in recovery below the desired altitude.
3.
Failure to adjust antitorque pedal pressures for changes
in power.
Ground Reference Maneuvers
Ground reference maneuvers may be used as training
exercises to help develop a division of attention between
the flightpath and ground references, and while controlling
the helicopter and watching for other air­craft in the vicinity.
Other examples of ground reference maneuvers are flights
for photographic or observation purposes, such as pipe line
or power line checks. Prior to each maneuver, a clearing
turn should be accomplished to ensure the area is free of
conflicting traffic.
Rectangular Course
The rectangular course is a training maneuver in which the
ground track of the helicopter is equidistant from all sides of a
selected rectangular area on the ground. While performing the
maneuver, the altitude and air­speed should be held constant.
The rectangular course helps develop recognition of a drift
toward or away from a line parallel to the intended ground
track. This is helpful in recognizing drift toward or from an
airport runway during the various legs of the airport traffic
pattern, and is also useful in observation and photographic
flights.
Technique
Maintaining ground track while trying to fly a straight line
can be very difficult for new pilots to do. It is important to
understand the effects of the wind and how to compensate
for this. For this maneuver, pick a square or rectangular field,
or an area bounded on four sides by section lines or roads,
with sides approximately a mile in length. The area selected
should be well away from other air traffic. Fly the maneuver
approximately 500 to 800 feet above the ground, which is
the altitude usually required for an airport traffic pattern. If
the student finds it difficult to maintain a proper ground track
at that higher altitude, lower the altitude for better ground
reference until they feel more comfortable and are able to
grasp the concept better. Altitude can be varied up to 800
feet as proficiency improves.
Fly the helicopter parallel to and at a uniform distance, about
one-fourth to one-half mile, from the field boundaries, and
not directly above the boundaries. For best results, position
flightpath outside the field boundaries just far enough away
that they may be easily observed from either pilot seat by
looking out the side of the helicopter. If an attempt is made
to fly directly above the edges of the field, there will be no
9-14
usable reference points to start and complete the turns. In
addition, the closer the track of the helicop­ter is to the field
boundaries, the steeper the bank necessary at the turning
points. The edges of the selected field should be seen while
seated in a normal position and looking out the side of the
helicopter during either a left-hand or right-hand course. The
distance of the ground track from the edges of the field should
be the same regardless of whether the course is flown to the
left or right. All turns should be started when the helicopter is
abeam the corners of the field boundaries. The bank nor­mally
should not exceed 30°–45° in light winds. Strong winds may
require more bank.
The pilot should understand that when trying to fly a straight
line and maintain a specific heading, aircraft heading must be
adjusted in order to compensate for the winds and stay on the
proper ground track. Also, keep in mind that a constant scan
of flight instruments and outside references aid in maintaining
proper ground track.
Although the rectangular course may be entered from any
direction, this discussion assumes entry on a downwind
heading. [Figure 9-15] while approaching the field boundary
on the downwind leg, begin planning for an upcoming turn.
Since there is a tailwind on the downwind leg, the helicopter’s
groundspeed is increased (position 1). During the turn, the
wind causes the heli­copter to drift away from the field. To
counteract this effect, the roll-in should be made at a fairly
fast rate with a relatively steep bank (position 2). This is
normally the steepest turn of the maneuver.
As the turn progresses, the tailwind component decreases,
which decreases the groundspeed. Consequently, the bank
angle and rate-of-turn must be reduced gradually to ensure
that upon completion of the turn, the crosswind ground track
continues to be the same distance from the edge of the field.
Upon completion of the turn, the helicopter should be level
and crabbed into the wind in order to maintain the proper
ground track. Keep in mind that in order to maintain proper
ground track the helicopter may have to be flown almost
sideways depending on the amount of wind. The forward
cyclic that is applied for airspeed will be in the direction of
the intended flight path. For this example, it will be in the
direction of the downwind corner of the field. However, since
the wind is now pushing the helicopter away from the field,
establish the proper drift correction by heading slightly into
the wind. Therefore, the turn should be greater than a 90°
change in heading (position 3). If the turn has been made
properly, the field boundary again appears to be one-fourth
to one-half mile away. While on the crosswind leg, the wind
correction should be adjusted, as necessary, to maintain a
uniform distance from the field boundary (position 4).
Enter 45° to downwind
No crab
Start turn at boundary
2
Complete turn at boundary
1
11
Turn more than 90°
10
Turn more than 90°—roll
out with crab established
Tra
3
tion
Crab into wind
c or
rec
Wind
tion
4
Tra
ck
Start turn
at boundary
ind
ow
with
no
win
dc
orre
c
ith n
ck w
Complete turn at boundary
Crab into wind
Turn less than 90°—roll out with crab established
Start turn
at boundary
Complete turn at boundary
9
Turn less than 90°
5
6
7
Complete turn at boundary
8
No crab
Start turn at boundary
Figure 9-15. Example of a rectangular course.
As the next field boundary is being approached (position 5),
plan for the next turn. Since a wind correction angle is being
held into the wind and toward the field, this next turn requires
a turn of less than 90°. Since there is now a headwind, the
groundspeed decreases during the turn, the bank initially must
be medium and progressively decrease as the turn pro­ceeds.
To complete the turn, time the rollout so that the helicopter
becomes level at a point aligned with the corner of the field
just as the longitudinal axis of the helicopter again becomes
parallel to the field boundary (position 6). The distance from
the field boundary should be the same as on the other sides
of the field.
Continue to evaluate each turn and determine the steepness
or shallowness based on the winds. It is also important to
remember that as the bank angles are adjusted in the turn,
the pilot is subsequently forced to make changes with the
flight controls.
Common Errors
1.
Faulty entry technique.
2.
Poor planning, orientation, and/or division of attention.
3.
Uncoordinated flight control application.
4.
Improper correction for wind drift.
5.
Failure to maintain selected altitude and airspeed.
6.
Selection of a ground reference with no suitable
emergency landing area within gliding distance.
7.
Not flying a course parallel to the intended area (e.g.,
traffic pattern or square field).
S-Turns
Another training maneuver to use is the S-turn, which helps
correct for wind drift in turns. This maneuver requires turns
to the left and right.
Technique
The pilot can choose to use a road, a fence, or a railroad
for a reference line. Regardless of what is used, it should
be straight for a considerable distance and should extend
as nearly perpendicular to the wind as possible. The object
of S-turns is to fly a pattern of two half cir­cles of equal size
on opposite sides of the reference line. [Figure 9-16] The
9-15
Wind
is to an upwind heading, the shallower the bank. In addition
to varying the angle of bank to correct for drift in order to
maintain the proper radius of turn, the helicopter must also
be flown with a drift correction angle (crab) in relation to its
ground track; except, of course, when it is on direct upwind
or downwind headings or there is no wind.
3
2
1
4
Points of steepest bank
Points of shallowest bank
5
Point of steepest bank
Figure 9-16. S-turns across a road.
maneuver should be performed at a constant altitude between
500 and 800 feet above the terrain. As mentioned previously,
if the student pilot is having a difficult time maintaining the
proper altitude and airspeed, have him or her attempt the
S-turn at a lower altitude, providing better ground reference.
The discussion that follows is based on choosing a reference
line perpendicular to the wind and starting the maneuver with
the helicopter facing downwind.
As the helicopter crosses the reference line, immedi­
ately establish a bank. This initial bank is the steepest
used throughout the maneuver since the helicopter is
headed directly downwind and the groundspeed is greatest
(position 1). Gradually reduce the bank, as necessary, to
describe a ground track of a half circle. Time the turn so
that, as the rollout is completed, the helicopter is crossing
the reference line perpendicular to it and head­ing directly
upwind (position 2). Immediately enter a bank in the opposite
direction to begin the second half of the “S” (position 3).
Since the helicopter is now on an upwind heading, this bank
(and the one just completed before crossing the reference
line) is the shallowest in the maneuver. Gradually increase
the bank, as necessary, to describe a ground track that is a
half circle identical in size to the one previously completed on
the other side of the refer­ence line (position 4). The steepest
bank in this turn should be attained just prior to rollout when
the helicopter is approaching the reference line nearest the
downwind heading. Time the turn so that as the rollout is
com­plete, the helicopter is perpendicular to the reference
line and is again heading directly downwind (position 5).
In summary, the angle of bank required at any given
point in the maneuver is dependent on the ground­speed.
The faster the groundspeed is, the steeper the bank is; the
slower the groundspeed is, the shallower the bank is. To
express it another way, the more nearly the helicopter is to a
downwind heading, the steeper the bank; the more nearly it
9-16
One would normally think of the fore and aft axis of the
heli­copter as being tangent to the ground track pattern at
each point. However, this is not the case. During the turn on
the upwind side of the reference line (side from which the
wind is blowing), crab the nose of the heli­copter toward the
outside of the circle. During the turn on the downwind side
of the reference line (side of the reference line opposite to the
direction from which the wind is blowing), crab the nose of
the helicopter toward the inside of the circle. In either case, it
is obvious that the helicopter is being crabbed into the wind
just as it is when trying to maintain a straight ground track.
The amount of crab depends on the wind velocity and how
close the helicopter is to a crosswind position. The stronger
the wind is, the greater the crab angle is at any given position
for a turn of a given radius. The more nearly the helicopter
is to a crosswind position, the greater the crab angle. The
maximum crab angle should be at the point of each half circle
farthest from the reference line.
A standard radius for S-turns cannot be specified, since the
radius depends on the airspeed of the helicopter, the velocity
of the wind, and the initial bank chosen for entry. The only
standard is crossing the ground reference line straight and
level, and having equal radius semi-circles on both sides.
Common Errors
1.
Using antitorque pedal pressures to assist turns.
2.
Slipping or skidding in the turn.
3.
An unsymmetrical ground track during S-turns across
a road.
4.
Improper correction for wind drift.
5.
Failure to maintain selected altitude or airspeed.
6.
Excessive bank angles.
Turns Around a Point
This training maneuver requires flying constant radius
turns around a preselected point on the ground using a bank
angle of approximately 30°–45°, while maintaining both
a constant altitude and the same distance from the point
throughout the maneuver. [Figure 9-17] The objective, as in
other ground reference maneuvers, is to develop the ability
to subconsciously control the helicopter while dividing
attention between flightpath, how the winds are affecting
the turn and ground references, and watching for other air
Wind
Steeper bank
d half of cir
cle
win
p
U
Steepest bank
Shallowest bank
Do
wn
le
wind h lf of circ
a
Shallower bank
Just as S-turns require that the helicopter be turned into the
wind in addition to varying the bank, so do turns around a
point. During the downwind half of the circle, the helicopter’s
nose must be progressively turned toward the inside of the
circle; during the upwind half, the nose must be progressively
turned toward the outside. The downwind half of the turn
around the point may be compared to the downwind side of
the S-turn, while the upwind half of the turn around a point
may be compared to the upwind side of the S-turn.
Upon gaining experience in performing turns around a point
and developing a good understanding of the effects of wind
drift and varying of the bank angle and wind correction angle
as required, entry into the maneuver may be from any point.
When entering this maneuver at any point, the radius of the
turn must be carefully selected, taking into account the wind
velocity and groundspeed so that an excessive bank is not
required later to maintain the proper ground track.
S-Turn Common Errors
Figure 9-17. Turns around a point.
traffic in the vicinity. This is also used in high reconnaissance,
observation, and photography flight.
Technique
The factors and principles of drift correction that are involved
in S-turns are also applicable to this maneu­ver. As in other
ground track maneuvers, a constant radius around a point
requires the pilot to change the angle of bank constantly
and make numerous control changes to compensate for
the wind. The closer the helicopter is to a direct downwind
heading at which the groundspeed is greatest, the steeper the
bank and the greater the rate of turn required to establish the
proper wind correc­tion angle. The closer the helicopter is to
a direct upwind heading at which the groundspeed is least,
the shallower the bank and the lower the rate of turn required
to establish the proper wind correction angle. Therefore,
throughout the maneuver, the bank and rate of turn must
be varied gradually and in proportion to the groundspeed
corrections made for the wind.
The point selected for turns should be prominent and easily
distinguishable, yet small enough to present a precise
reference. Isolated trees, crossroads, or other similar small
landmarks are usually suitable. The point should be in an area
away from communities, livestock, or groups of people on
the ground to prevent possible annoyance or hazard to others.
Since the maneuver is performed between 500 and 800 feet
AGL, the area selected should also afford an opportu­nity
for a safe emergency autorotation in the event it becomes
necessary.
1.
Faulty entry technique.
2.
Poor planning, orientation, or division of attention.
3.
Uncoordinated flight control application.
4.
Improper correction for wind drift.
5.
Failure to maintain selected altitude or airspeed.
6.
Failure to maintain an equal distance around the point.
7.
Excessive bank angles.
Traffic Patterns
A traffic pattern promotes safety by establishing a common
track to help pilots determine their landing order and provide
common reference. A traffic pattern is also useful to control
the flow of traffic, par­ticularly at airports without operating
control towers. It affords a measure of safety, separation,
protection, and administrative control over arriving,
departing, and circling aircraft. Due to specialized operating
character­istics, airplanes and helicopters do not mix well
in the same traffic environment. At multiple-use airports,
regulation states that helicopters should always avoid the
flow of fixed-wing traf­fic. To do this, be familiar with the
patterns typically flown by airplanes. In addition, learn how
to fly these patterns in case air traf­fic control (ATC) requests
a fixed-wing traffic pattern be flown.
A normal airplane traffic pattern is rectangular, has five named
legs, and a designated altitude, usually 1,000 feet AGL. While
flying the traffic pattern, pilots should always keep in mind
noise abatement rules and flying friendly to avoid dwellings
9-17
and livestock. A pattern in which all turns are to the left is
called a standard pattern. [Figure 9-18] The takeoff leg (item
1) normally consists of the aircraft’s flightpath after takeoff.
This leg is also called the upwind leg. Turn to the crosswind
leg (item 2) after passing the departure end of the runway when
at a safe altitude. Fly the downwind leg (item 3) parallel to the
runway at the designated traffic pattern altitude and distance
from the runway. Begin the base leg (item 4) at a point selected
according to other traffic and wind conditions. If the wind is
very strong, begin the turn sooner than normal. If the wind
is light, delay the turn to base. The final approach (item 5)
is the path the air­craft flies immediately prior to touchdown.
Traffic pattern entry procedures at an airport with an operating
control tower are specified by the controller. At uncontrolled
airports, traffic pattern altitudes and entry procedures may
vary according to established local procedures. Helicopter
pilots should be aware of the standard airplane traffic
pattern and avoid it. Generally, helicopters make a lower
altitude pattern opposite from the fixed wing pattern and
make their approaches to some point other than the runway
in use by the fixed wing traffic. Chapter 7 of the Airplane
flying Handbook, FAA-H-8083-3 discusses this in greater
detail. For information concerning traffic pattern and landing
direction, utilize airport advisory service or UNICOM, when
available.
3 Downwind leg
The standard departure procedure when using the fixedwing traffic pattern is usually a straight-out, down­wind, or
right-hand departure. When a control tower is in operation,
request the type of departure desired. In most cases, helicopter
departures are made into the wind unless obstacles or traffic
dictate otherwise. At airports without an operating control
tower, comply with the departure procedures established for
that airport, if any.
Base leg
4
2 Crosswind leg
09
5 Final approach leg
1 Takeoff leg (upwind)
Figure 9-18. A standard fixed-wing traffic pattern consists of left
turns, has five designated legs, and is flown at 1,000' AGL.
Flying a fixed wing traffic pattern at 1,000 feet AGL upon
the request of ATC should not be a problem for a helicopter
unless conducting specific maneuvers that require specific
altitudes. There are variations at different localities and at
airports with operating control towers. For example, air traffic
control (ATC) may have airplanes in a left turn pattern as
airplane pilots are usually seated in the left seat and a right
turn pattern for helicopters as those pilots are usually in the
right seat. This arrangement affords the best view from each
of the cockpits. Always consult the Airport/Facility Directory
for the traffic pattern procedures at your airport/heliport.
An accepted helicopter traffic pattern is flown at 500 feet
AGL and consists of right turns. [Figure 9-19] This keeps the
helicopter out of the flow of fixed-wing traffic. A helicopter
may take off from a helipad into the wind with a turn to the
right after 300 feet AGL or as needed to be in range of forced
landing areas. When 500 feet AGL is attained, a right turn
to parallel the takeoff path is made for the downwind. Then,
as the intended landing point is about 45 degrees behind the
abeam position of the helicopter, a right turn is made and a
descent is begun from downwind altitude to approximately
300 feet AGL for a base leg.
3 Downwind leg
4 Base leg
1.
The helicopter’s call sign, “Helicopter 8340J.”
2.
The helicopter’s position, “10 miles west.”
3.
The “request for landing and hover to ...”
To avoid the flow of fixed-wing traffic, the tower often
clears direct to an approach point or to a particular runway
intersection nearest the destination point. At uncontrolled
airports, if at all possible, adhere to standard practices and
patterns.
9-18
Crosswind leg
2
27
When approaching an airport with an operating control tower
in a helicopter, it is possible to expedite traffic by stating
intentions. The communication consists of:
1 Takeoff leg (upwind)
5 Final approach leg
Figure 9-19. A standard helicopter traffic pattern consists of right
turns, has 5 designated legs, and is flown at 500' AGL.
As the helicopter nears the final approach path, the turn to
final should be made considering winds and obstructions.
Depending on obstructions and forced landing areas, the final
approach may need to be accomplished from as high as 500
feet AGL. The landing area should always be in sight and
the angle of approach should never be too high (indicating
that the base leg is too close) to the landing area or too low
(indicating that the landing area is too far away).
Reference point
Approaches
An approach is the transition from traffic pattern alti­tude
to either a hover or to the surface. The approach should
terminate at the hover altitude with the rate of descent and
groundspeed reaching zero at the same time. Approaches
are categorized according to the angle of descent as normal,
steep, or shallow. In this chapter, concentration is on the
normal approach. Steep and shallow approaches are discussed
in the next chapter.
Imaginary centerline
Use the type of approach best suited to the existing conditions.
These conditions may include obstacles, size and surface of
the landing area, density altitude, wind direction and speed,
and weight. Regardless of the type of approach, it should
always be made to a specific, predetermined landing spot.
Normal Approach to a Hover
A normal approach uses a descent profile of between 7° and
12° starting at approximately 300–500 feet AGL.
Technique
On final approach, at the recommended approach airspeed
and at approximately 300 feet AGL, the helicopter should
be on the correct ground track (or ground alignment) for
the intended landing site, but the axis of the helicopter does
not have to be aligned until about 100' AGL to facilitate a
controlled approach. [Figure 9-20] Just prior to reaching
the desired approach angle, begin the approach by lowering
the collective sufficiently to get the helicopter decelerating
and descending down the approach angle. With the decrease
in the collective, the nose tends to pitch down, requiring
aft cyclic to maintain the recommended approach airspeed
attitude. Adjust antitorque pedals, as necessary, to maintain
trim. Pilots should visualize the angle from the landing
point to the middle of the skids or landing gear underneath
them in the cockpit and maneuver the helicopter down that
imaginary slope until the helicopter is at a hover centered
over the landing point, or touching down centered on the
landing point. The most important standard for a normal
approach is maintaining a consistent angle of approach to
the termination point. The collective controls the angle of
approach. Use the cyclic to control the rate of closure or how
fast the helicopter is moving towards the touchdown point.
Maintain entry airspeed until the apparent groundspeed and
rate of closure appear to be increasing. At this point, slowly
begin decelerating with slight aft cyclic, and smoothly lower
Figure 9-20. Plan the turn to final so the helicopter rolls out on an
imaginary extension of the centerline for the final approach path.
This path should neither angle to the landing area, as shown by
the helicopter on the left, nor require an S-turn, as shown by the
helicopter on the right.
the collective to maintain approach angle. Use the cyclic to
maintain a rate of closure equivalent to a brisk walk.
At approximately 25 knots, depending on wind, the helicopter
begins to lose effective translational lift. To compensate for
loss of effective translational lift, increase the collective to
maintain the approach angle, while maintaining the proper
rpm. The increase of collective pitch tends to make the nose
rise, requiring forward cyclic to maintain the proper rate of
closure.
As the helicopter approaches the recommended hover
altitude, increase the collective sufficiently to maintain the
hover. Helicopters require near maximum power to land
because the inertia of the helicopter in a descent must be
overcome by lift in the rotor system. At the same time, apply
aft cyclic to stop any forward movement while controlling
the heading with antitorque pedals.
9-19
Common Errors
1.
Failing to maintain proper rpm during the entire
approach.
2.
Improper use of the collective in controlling the angle
of descent.
3.
Failing to make antitorque pedal corrections to
compensate for collective changes during the
approach.
4.
Maintaining a constant airspeed on final approach
instead of an apparent brisk walk.
5.
Failing to simultaneously arrive at hovering alti­tude
and attitude with zero groundspeed.
Crosswind During Approaches
During a crosswind approach, crab into the wind. At
approximately 50 feet of altitude, use a slip to align the
fuselage with the ground track. The rotor is tilted into the
wind with cyclic pressure so that the sideward movement
of the helicopter and wind drift counteracts each other.
Maintain the heading and ground track with the antitorque
pedals. Under crosswind approaches, ground track is always
controlled by the cyclic movement. The heading of the
helicopter in hovering maneuvers is always controlled by
the pedals. The collective controls power, which is altitude
at a hover. This technique should be used on any type of
crosswind approach, whether it is a shallow, normal, or
steep approach.
6.
Low rpm in transition to the hover at the end of the
approach.
Go-Around
7.
Using too much aft cyclic close to the surface, which
may result in tail rotor strikes.
8.
Failure to crab above 100’AGL and slip below
100’AGL.
A go-around is a procedure for remaining airborne after
an intended landing is discontinued. A go-around may be
necessary when:
Normal Approach to the Surface
A normal approach to the surface or a no-hover landing is
often used if loose snow or dusty surface conditions exist.
These situations could cause severely restricted visibility, or
the engine could possibly ingest debris when the heli­copter
comes to a hover. The approach is the same as the normal
approach to a hover; however, instead of termi­nating at a
hover, continue the approach to touchdown. Touchdown
should occur with the skids level, zero groundspeed, and a
rate of descent approaching zero.
Technique
As the helicopter nears the surface, increase the collec­tive, as
necessary, to cushion the landing on the sur­face, terminate in
a skids-level attitude with no forward movement.
Common Errors
1.
Terminating to a hover, and then making a vertical
landing.
2.
Touching down with forward movement.
3.
Approaching too slow, requiring the use of exces­sive
power during the termination.
4.
Approaching too fast, causing a hard landing
5.
Not maintaining skids aligned with direction of travel
at touchdown. Any movement or misalignment of the
skids or gear can induce dynamic rollover
9-20
•
Instructed by the control tower.
•
Traffic conflict occurs.
•
The helicopter is in a position from which it is not
safe to continue the approach. Any time an approach
is uncomfortable, incorrect, or potentially dangerous,
abandon the approach. The deci­sion to make a goaround should be positive and initiated before a critical
situation develops. When the decision is made, carry it
out without hesitation. In most cases, when initiating
the go-around, power is at a low setting. Therefore,
the first response is to increase collective to takeoff
power. This movement is coordinated with the throttle
to maintain rpm, and with the proper antitorque pedal
to control heading. Then, establish a climb attitude
and maintain climb speed to go around for another
approach.
Chapter Summary
This chapter introduced basic flight maneuvers and the
techniques to perform each of them. Common errors and why
they happen were also described to help the pilot achieve a
better understanding of the maneuver.
Chapter 10
Advanced
Flight Maneuvers
Introduction
The maneuvers presented in this chapter require more skill
and understanding of the helicopter and the surrounding
environment. When performing these maneuvers, a pilot
is probably taking the helicopter to the edge of the safe
operating envelope. Therefore, if you are ever in doubt about
the outcome of the maneuver, abort the mission entirely or
wait for more favorable conditions.
10-1
Reconnaissance Procedures
When planning to land or take off at an unfa­miliar site,
gather as much information as possible about the area.
Reconnaissance techniques are ways of gathering this
information.
High Reconnaissance
The purpose of conducting a high reconnaissance is to
determine direction and speed of the wind, a touchdown
point, suitability of the landing area, approach and departure
axes, and obstacles for both the approach and departure.
The pilot should also give particular consideration to forced
landing areas in case of an emergency.
Altitude, airspeed, and flight pattern for a high recon­naissance
are governed by wind and terrain features. It is important to
strike a balance between a reconnaissance conducted too high
and one too low. It should not be flown so low that a pilot
must divide attention between studying the area and avoiding
obstructions to flight. A high reconnaissance should be flown
at an alti­tude of 300 to 500 feet above the surface. A general
rule to follow is to ensure that sufficient altitude is available
at all times to land into the wind in case of engine fail­ure. In
addition, a 45° angle of observation generally allows the best
estimate of the height of barriers, the presence of obstacles,
the size of the area, and the slope of the terrain. Always
maintain safe altitudes and air­speeds, and keep a forced
landing area within reach whenever possible.
Low Reconnaissance
A low reconnaissance is accomplished during the approach to
the landing area. When flying the approach, verify what was
observed in the high recon­naissance, and check for anything
new that may have been missed at a higher altitude, such as
wires and their supporting structures (poles, towers, etc.),
slopes, and small crevices. If the pilot determines that the
area chosen is safe to land in, the approach can be continued.
However, the decision to land or go around must be made
prior to decelerating below effective translational lift (ETL),
or before descending below the barriers surrounding the
confined area.
If a decision is made to complete the approach, termi­nate
the landing to a hover in order to check the landing point
carefully before lowering the helicopter to the surface.
Under certain conditions, it may be desirable to continue the
approach to the surface. Once the heli­copter is on the ground,
maintain operating rpm until the stability of the helicopter
has been checked to be sure it is in a secure and safe position.
Ground Reconnaissance
Prior to departing an unfamiliar location, make a detailed
analysis of the area. There are several factors to consider
10-2
during this evaluation. Besides determining the best departure
path and indentifying all hazards in the area, select a route
that gets the helicopter from its present position to the take­off
point while avoiding all hazards, especially to the tail rotor
and landing gear.
Some things to consider while formulating a takeoff plan
are the aircraft load, height of obstacles, the shape of the
area, direction of the wind, and surface conditions. Surface
conditions can consist of dust, sand and snow, as well as
mud and rocks. Dust landings and snow landings can lead
to a brownout or whiteout condition, which is the loss of
the horizon reference. Disorientation may occur, leading
to ground contact, often with fatal results. Taking off or
landing on uneven terrain, mud, or rocks can cause the tail
rotor to strike the surface or if the skids get caught can lead
to dynamic rollover. If the helicopter is heavily loaded,
determine if there is sufficient power to clear the obstacles.
Sometimes it is better to pick a path over shorter obstacles
than to take off directly into the wind. Also evaluate the shape
of the area so that a path can be chosen that will provide you
the most room to maneuver and abort the take­off if necessary.
Positioning the helicopter to the most downwind portion of
the confined area gives the pilot the most distance to clear
obstacles. Wind analysis also helps determine the route of
takeoff. The prevailing wind can be altered by obstructions
on the departure path and can significantly affect aircraft
performance. There are several ways to check the wind
direction before taking off. One technique is to watch the tops
of the trees; another is to look for any smoke in the area. If
there is a body of water in the area, look to see which way the
water is rippling. If wind direction is still in question revert
back to the last report that was received by either ATIS or
airport tower.
Maximum Performance Takeoff
A maximum performance takeoff is used to climb at a steep
angle to clear barriers in the flightpath. It can be used when
taking off from small areas surrounded by high obstacles.
Allow for a vertical takeoff, although not preferred, if
obstruction clearance could be in doubt. Before attempting
a maximum performance takeoff, know thoroughly the
capabilities and limitations of the equipment. Also consider
the wind velocity, temperature, density alti­tude, gross weight,
center of gravity (CG) location, and other factors affecting
pilot technique and the perform­ance of the helicopter.
To accomplish this type of takeoff safely, there must be
enough power to hover OGE in order to prevent the helicopter
from sinking back to the surface after becoming airborne.
A hover power check can be used to deter­mine if there is
sufficient power available to accomplish this maneuver.
The angle of climb for a maximum performance take­
off depends on existing conditions. The more critical the
conditions are, such as high density altitudes, calm winds,
and high gross weights, the shallower the angle of climb is. In
light or no wind conditions, it might be necessary to operate
in the crosshatched or shaded areas of the height/velocity
diagram during the begin­ning of this maneuver. Therefore,
be aware of the calculated risk when operating in these areas.
An engine failure at a low altitude and airspeed could place
the helicopter in a dangerous position, requiring a high degree
of skill in making a safe autorotative landing.
Technique
Before attempting a maximum performance takeoff,
reposition the helicopter to the most downwind area to allow a
longer takeoff climb, then bring the helicopter to a hover, and
determine the excess power available by noting the difference
between the power available and that required to hover.
Also, perform a balance and flight control check and note
the position of the cyclic. If the takeoff path allows, position
the helicopter into the wind and return the helicopter to the
surface. Normally, this maneuver is initiated from the surface.
After checking the area for obstacles and other aircraft, select
reference points along the takeoff path to maintain ground
track. Also consider alternate routes in case the maneuver is
not possible. [Figure 10-1]
5
4
in pedal pressure to maintain heading (position 2). Use the
cyclic, as necessary, to control movement toward the desired
flightpath and, therefore, climb angle during the maneuver
(position 3). Maintain rotor rpm at its maxi­mum, and do
not allow it to decrease since you would probably need to
lower the collective to regain it. Maintain these inputs until
the helicopter clears the obstacle, or until reaching 50 feet
for demonstration purposes (position 4). Then, establish a
normal climb attitude and power setting (position 5). As
in any maximum performance maneuver, the techniques
used affect the actual results. Smooth, coordinated inputs
coupled with precise control allow the helicopter to attain
its maximum performance.
An acceptable but less preferred variation is to perform a
vertical takeoff. This technique allows the pilot to descend
vertically back into the confined area if the helicopter
does not have the performance to clear the surrounding
obstacles. During this maneuver, the helicopter must climb
vertically and not be allowed to accelerate forward until the
surrounding obstacles have been cleared. If not, a situation
may develop where the helicopter does not have sufficient
climb performance to avoid obstructions and may not have
power to descend back to the takeoff point. The vertical
takeoff might not be as efficient as the climbing profile, but
is much easier to abort from a vertical position directly over
the landing point. The vertical takeoff however places the
helicopter in the avoid are of the height/velocity diagram for
a longer time. This maneuver requires hover OGE power to
accomplish.
Common Errors
1.
Failure to consider performance data, including height/
velocity diagram.
2.
Nose too low initially causing horizontal flight rather
than more vertical flight.
3.
Failure to maintain maximum permissible rpm.
4.
Abrupt control movements.
5.
Failure to resume normal climb power and air­speed
after clearing the obstacle.
3
2
1
Figure 10-1. Maximum performance takeoff.
Begin the takeoff by getting the helicopter light on the
skids (position 1). Pause and neutralize all aircraft move­
ment. Slowly increase the collective and position the
cyclic to lift off in a 40 knot attitude. This is approximately
the same attitude as when the helicopter is light on the
skids. Continue to increase the collec­tive slowly until the
maximum power available is reached (takeoff power is
normally 10 percent above power required for hover). This
large collective movement requires a substantial increase
Running/Rolling Takeoff
A running takeoff in helicopter with fixed landing gear,
such as skids, skis or floats, or a rolling takeoff in a
wheeled helicopter is sometimes used when conditions of
load and/or density altitude prevent a sus­tained hover at
normal hovering altitude. For wheeled helicopters, a rolling
takeoff is sometimes used to minimize the downwash
created during a takeoff from a hover. Avoid a running/
rolling maneuver if there is not sufficient power to hover,
at least momentarily. If the helicopter cannot be hovered,
10-3
its performance is unpredictable. If the helicopter cannot
be raised off the surface at all, sufficient power might not
be available to accomplish the maneuver safely. If a pilot
cannot momentarily hover the helicopter, wait for conditions
to improve or off-load some of the weight.
The height/velocity parameters should be respected at all
times. The helicopter should be flown to a suitable altitude
to allow a safe acceleration in accordance with the height/
velocity diagram.
Common Errors
To accomplish a safe running or rolling takeoff, the sur­face
area must be of sufficient length and smoothness, and there
cannot be any barriers in the flightpath to interfere with a
shallow climb.
1.
Failing to align heading and ground track to keep
surface friction to a minimum.
2.
Attempting to become airborne before obtaining
effective translational lift.
Technique
Refer to Figure 10-2. To begin the maneuver, first align the
helicopter to the takeoff path. Next, increase the throttle to
obtain takeoff rpm, and increase the collec­tive smoothly
until the helicopter becomes light on the skids or landing
gear (position 1). If taking off from the water, ensure that
the floats are mostly out of the water. Then, move the cyclic
slightly forward of the neutral hovering position, and apply
additional collective to start the forward movement (position
2). To simulate a reduced power condition during practice,
use one to two inches less manifold pressure, or three to five
percent less torque than that required to hover. The landing
3.
Using too much forward cyclic during the surface run.
4.
Lowering the nose too much after becoming air­borne,
resulting in the helicopter settling back to the surface.
5.
Failing to remain below the recommended altitude
until airspeed approaches normal climb speed.
1
2
3
4
Figure 10-2. Running/rolling takeoff.
gear must stay aligned with the takeoff direction until the
helicopter leaves the surface to avoid dynamic rollover.
Maintain a straight ground track with lateral cyclic and
heading with antitorque pedals until a climb is established.
As effective translational lift is gained, the helicopter
becomes airborne in a fairly level attitude with little or no
pitching (position 3). Maintain an altitude to take advan­tage
of ground effect, and allow the airspeed to increase toward
normal climb speed. Then, follow a climb profile that takes
the helicopter through the clear area of the height/velocity
diagram (position 4). During practice maneuvers, after having
climbed to an altitude of 50 feet, establish the normal climb
power setting and attitude.
NOTE: It should be remembered that if a running takeoff is
necessary for most modern helicopters, the helicopter is very
close to, or has exceeded the maximum operating weight for
the conditions (i.e., temperature and altitude).
10-4
Rapid Deceleration or Quick Stop
This maneuver is used to decelerate from forward flight to a
hover. It is often used to abort takeoffs, to stop if something
blocks the helicopter flightpath, or simply to terminate an air
taxi maneuver, as mentioned in the Aeronautical Information
Manual (AIM). A quick stop is usually practiced on a runway,
taxiway, or over a large grassy area away from other traffic
or obstacles.
Technique
The maneuver requires a high degree of coordination of
all controls. It is practiced at an altitude that permits a safe
clearance between the tail rotor and the surface throughout
the maneuver, especially at the point where the pitch attitude
is highest. The altitude at completion should be no higher
than the maximum safe hovering altitude prescribed by that
particular helicopter’s manufacturer. In selecting an altitude
at which to begin the maneuver, take into account the overall
length of the helicopter and its height-velocity diagram. Even
though the maneuver is called a rapid deceleration or quick
stop, it is performed slowly and smoothly with the primary
emphasis on coordination.
During training, always perform this maneuver into the wind
[Figure 10-3, position 1]. After leveling off at an altitude
between 25 and 40 feet, depending upon the manufacturer’s
recommendations, accelerate to the desired entry speed,
which is approximately 45 knots for most training helicopters
(position 2). The altitude chosen should be high enough to
avoid danger to the tail rotor during the flare, but low enough
to stay out of the hazardous areas of that helicopter’s heightvelocity diagram throughout the maneuver. In addition, this
altitude should be low enough that the helicopter can be
brought to a hover during the recovery.
1
2
4
3
5
Figure 10-3. Rapid deceleration or quick stop.
At position 3, initiate the deceleration by applying aft cyclic
to reduce forward groundspeed. Simultaneously, lower the
collective, as necessary, to counteract any climbing tendency.
The timing must be exact. If too little collective is taken out
for the amount of aft cyclic applied, the helicopter climbs.
If too much downward collective is applied, the helicopter
will descend. A rapid application of aft cyclic requires an
equally rapid application of down collective. As collective
pitch is lowered, apply proper antitorque pedal pressure to
maintain heading, and adjust the throttle to maintain rpm.
The G loading on the rotor system depends on the pitch-up
attitude. If the attitude is too high, the rotor system may stall
and cause the helicopter to impact the surface.
After attaining the desired speed (position 4), initiate the
recovery by lowering the nose and allowing the helicopter
to descend to a normal hovering altitude in level flight and
zero groundspeed (position 5). During the recovery, increase
collective pitch, as necessary, to stop the helicopter at normal
hovering altitude, adjust the throttle to maintain rpm, and apply
proper antitorque pedal pressure, as necessary, to maintain
heading. During the maneuver, visualize rotating around the
tail rotor until a normal hovering altitude is reached.
Common Errors
1.
Initiating the maneuver by lowering the collective
without aft cyclic pressure to maintain altitude.
2.
Initially applying aft cyclic stick too rapidly, causing
the helicopter to balloon (climb).
3.
Failing to effectively control the rate of deceleration
to accomplish the desired results.
4.
Allowing the helicopter to stop forward motion in a
tail-low attitude.
5.
Failing to maintain proper rotor rpm.
6.
Waiting too long to apply collective pitch (power)
during the recovery, resulting in excessive manifold
pressure or an overtorque situation when collective
pitch is applied rapidly.
7.
Failing to maintain a safe clearance over the terrain.
8.
Using antitorque pedals improperly, resulting in erratic
heading changes.
9.
Using an excessively nose-high attitude.
Steep Approach
A steep approach is used primarily when there are obstacles
in the approach path that are too high to allow a normal
approach. A steep approach permits entry into most confined
areas and is sometimes used to avoid areas of turbulence
around a pinnacle. An approach angle of approximately 13°
to 15° is considered a steep approach. [Figure 10-4] Caution
must be exercised to avoid the parameters for settling with
power (20–100 percent of available power applied, airspeed
of less than 10 knots, and a rate of descent greater than 300
fpm). For additional information on settling with power,
refer to Chapter 11, Helicopter Emergencies and Hazards.
1
2
15° Approach angle
3
4
Figure 10-4. Steep approach to a hover.
10-5
Technique
On final approach, maintain track with the intended
touchdown point and into the wind as much as possible at
the recommended approach airspeed (position 1). When
intercepting an approach angle of 13° to 15°, begin the
approach by lowering the collective sufficiently to start
the helicopter descending down the approach path and
decelerating (position 2). Use the proper antitorque pedal for
trim. Since this angle is steeper than a normal approach angle,
reduce the collective more than that required for a normal
approach. Continue to decelerate with slight aft cyclic and
smoothly lower the collective to maintain the approach angle.
The intended touchdown point may not always be visible
throughout the approach, especially when landing to a hover.
Pilots must learn to cue in to other references that are parallel
to the intended landing area that will help them maintain
ground track and position.
Constant management of approach angle and airspeed is
essential to any approach. Aft cyclic is required to decelerate
sooner than a normal approach, and the rate of closure
becomes apparent at a higher altitude. Maintain the approach
angle and rate of descent with the collective, rate of closure
with the cyclic, and trim with antitorque pedals.
The helicopter should be kept in trim just prior to loss of
effective translational lift (approximately 25 knots). Below
100' AGL, the antitorque pedals should be adjusted to align
the helicopter with the intended touchdown point. Visualize
the location of the tail rotor behind the helicopter and fly the
landing gear to 3 feet above the intended landing point. In
small confined areas, the pilot must precisely position the
helicopter over the intended landing area. Therefore, the
approach must stop at that point.
Loss of effective translational lift occurs higher in a steep
approach (position 3), requiring an increase in the collective
to prevent settling, and more forward cyclic to achieve
the proper rate of closure. Once the intended landing area
is reached, terminate the approach to a hover with zero
groundspeed (position 4). If the approach has been executed
properly, the helicopter will come to a halt at a hover altitude
of 3 feet over the intended landing point with very little
additional power required to hold the hover.
The pilot must aware that any wind effect is lost once the
aircraft has descended below the barriers surrounding a
confined area, causing the aircraft to settle more quickly.
Additional power may be needed on a strong wind condition
as the helicopter descends below the barriers.
Common Errors
1.
Failing to maintain proper rpm during the entire
approach.
2.
Using collective improperly in maintaining the
selected angle of descent.
3.
Failing to make antitorque pedal corrections to
compensate for collective pitch changes during the
approach.
4.
Slowing airspeed excessively in order to remain on
the proper angle of descent.
5.
Failing to determine when effective transla­tional lift
is being lost.
6.
Failing to arrive at hovering altitude and attitude, and
zero groundspeed almost simultaneously.
7.
Utilizing low rpm in transition to the hover at the end
of the approach.
8.
Using too much aft cyclic close to the surface, which
may result in the tail rotor striking the sur­face.
9.
Failure to align landing gear with direction of travel
no later than beginning of loss of translational lift.
Shallow Approach and Running/Roll-On
Landing
Use a shallow approach and running landing when a
high density altitude, a high gross weight condition, or
some combination thereof, is such that a normal or steep
approach cannot be made because of insufficient power
to hover. [Figure 10-5] To compensate for this lack of
power, a shallow approach and running landing makes use
of translational lift until surface contact is made. If flying a
wheeled helicopter, a roll-on landing can be used to minimize
the effect of downwash. The glide angle for a shallow
approach is approximately 3° to 5°. This angle is similar to
the angle used on an ILS approach. Since the helicopter is
sliding or rolling to a stop during this maneuver, the landing
area should be smooth and the landing gear must be aligned
with the direction of travel to prevent dynamic rollover and
must be long enough to accomplish this task. After landing,
ensure that the pitch of the rotor blades is not to far aft as the
main rotor blades could contact the tailboom.
5° Approach angle
1
2
3
Figure 10-5. Shallow approach and running landing.
10-6
4
Technique
A shallow approach is initiated in the same manner as the
normal approach except that a shallower angle of descent is
maintained. The power reduction to initiate the desired angle
of descent is less than that for a normal approach since the
angle of descent is less (position 1).
As the collective is lowered, maintain heading with proper
antitorque pedal pressure and rpm with the throttle. Maintain
approach airspeed until the apparent rate of closure appears
to be increasing. Then, begin to slow the helicopter with aft
cyclic (position 2).
As in normal and steep approaches, the primary control
for the angle and rate of descent is the collective, while the
cyclic primarily controls the groundspeed. However, there
must be a coordination of all the con­trols for the maneuver
to be accomplished successfully. The helicopter should
arrive at the point of touchdown at or slightly above effective
translational lift. Since translational lift diminishes rapidly
at slow airspeeds, the deceleration must be coordinated
smoothly, at the same time keeping enough lift to prevent
the helicopter from settling abruptly.
Just prior to touchdown, place the helicopter in a level attitude
with the cyclic, and maintain heading with the antitorque
pedals. Use the cyclic to direction of travel and ground track
identical (position 3). Allow the helicopter to descend gently
to the surface in a straight-­and-level attitude, cushioning the
landing with the collective. After surface contact, move the
cyclic slightly forward to ensure clearance between the tail
boom and the rotor disk. Use the cyclic to maintain the surface
track (position 4). A pilot normally holds the collective
stationary until the heli­copter stops; however, to get more
braking action, lower the collective slightly.
Keep in mind that, due to the increased ground friction when
the collective is lowered or if the landing is being executed
to a rough or irregular surface, the helicopter may come to
an abrupt stop and the nose might pitch forward. Exercise
caution not to correct this pitching movement with aft cyclic,
which could result in the rotor making contact with the tail
boom. An abrupt stop may also cause excessive transmission
movement resulting in the transmission contacting its mount.
During the landing, maintain normal rpm with the throttle
and directional control with the antitorque pedals.
For wheeled helicopters, use the same technique except after
landing, lower the collective, neutralize the controls, and
apply the brakes, as necessary, to slow the helicopter. Do not
use aft cyclic when bringing the helicopter to a stop.
Common Errors
1.
Assuming excessive nose-high attitude to slow the
helicopter near the surface.
2.
Utilizing insufficient collective and throttle to cushion
a landing.
3.
Failure to maintain heading resulting in a turning or
pivoting motion.
4.
Failure to add proper antitorque pedal as collec­tive is
added to cushion landing, resulting in a touchdown
while the helicopter is moving sideward.
5.
Failure to maintain a speed that takes advantage of
effective translational lift.
6.
Touching down at an excessive groundspeed for the
existing conditions. (Some helicopters have maximum
touchdown groundspeeds.)
7.
Failure to touch down in the appropriate attitude
necessary for a safe landing. Appropriate attitude is
based on the type of helicopter and the landing gear
installed.
8.
Failure to maintain proper rpm during and after
touchdown.
9.
Maintaining poor alignment with direction of travel
during touchdown.
Slope Operations
Prior to conducting any slope operations, be thoroughly
familiar with the characteristics of dynamic rollover and
mast bumping, which are dis­cussed in Chapter 12, Helicopter
Emergencies. The approach to a slope is similar to the
approach to any other landing area. During slope operations,
make allowances for wind, barriers, and forced landing sites
in case of engine failure. Since the slope may constitute
an obstruction to wind passage, anticipate turbulence and
downdrafts.
Slope Landing
A pilot usually lands a helicopter across the slope rather than
with the slope. Landing with the helicopter facing down
the slope or downhill is not recommended because of the
possibility of striking the tail rotor on the surface.
Technique
Refer to Figure 10-6. At the termination of the approach, if
necessary, move the helicopter slowly toward the slope, being
careful not to turn the tail upslope. Position the helicopter
across the slope at a stabilized hover headed into the wind
over the intended landing spot (frame 1). Downward pressure
10-7
1
2
4
3
Figure 10-6. Slope landing.
on the collective starts the helicopter descending. As the
upslope skid touches the ground, hesitate momentarily in a
level attitude, then apply slight lateral cyclic in the direction
of the slope (frame 2). This holds the skid against the slope
while the pilot continues lowering the downslope skid with
the col­lective. As the collective is lowered, continue to move
the cyclic toward the slope to maintain a fixed position (frame
3) The slope must be shallow enough to hold the helicopter
against it with the cyclic during the entire landing. A slope
of 5° is considered maxi­mum for normal operation of most
helicopters. Consult the RFM or POH for the specific
limitations of the helicopter being flown.
Be aware of any abnormal vibration or mast bumping that
signals maximum cyclic deflection. If this occurs, abandon
the landing because the slope is too steep. In most helicopters
with a counterclockwise rotor system, landings can be made
on steeper slopes when holding the cyclic to the right. When
landing on slopes using left cyclic, some cyclic input must
be used to overcome the translating tendency. If wind is not
a factor, consider the drifting tendency when determining
landing direction.
After the downslope skid is on the surface, reduce the
collective to full down, and neutralize the cyclic and pedals
(frame 4). Normal operating rpm should be maintained
until the full weight of the helicopter is on the landing gear.
1
Figure 10-7. Slope takeoff.
10-8
2
This ensures adequate rpm for immediate takeoff in case
the helicopter starts sliding down the slope. Use antitorque
pedals as necessary throughout the landing for heading
control. Before reducing the rpm, move the cyclic control as
neces­sary to check that the helicopter is firmly on the ground.
Common Errors
1.
Failing to consider wind effects during the approach
and landing.
2.
Failing to maintain proper rpm throughout the entire
maneuver.
3.
Failure to maintain heading resulting in a turning or
pivoting motion.
4.
Turning the tail of the helicopter into the
slope.
5.
Lowering the downslope skid or wheel too rapidly.
6.
Applying excessive cyclic control into the slope,
causing mast bumping.
Slope Takeoff
A slope takeoff is basically the reverse of a slope land­ing.
[Figure 10-7] Conditions that may be associated with the
slope, such as turbulence and obstacles, must be considered
during the takeoff. Planning should include suitable forced
landing areas.
3
Technique
Confined Area Operations
Begin the takeoff by increasing rpm to the normal range with
the collective full down. Then, move the cyclic toward the
slope (frame 1). Holding the cyclic toward the direction of
the slope causes the downslope skid to rise as the pilot slowly
raises the collective (frame 2). As the skid comes up, move
the cyclic as necessary to maintain a level attitude in relation
to the horizon. If properly coordinated, the helicopter should
attain a level attitude as the cyclic reaches the neutral position.
At the same time, use antitorque pedal pressure to maintain
heading and throttle to maintain rpm. With the helicopter
level and the cyclic centered, pause momentarily to verify
everything is correct, and then gradually raise the collective
to complete the liftoff (frame 3). After reaching a hover,
avoid hitting the ground with the tail rotor by not turning the
helicopter tail upslope and gaining enough altitude to ensure
the tail rotor is clear. If an upslope wind exists, execute a
crosswind takeoff and then make a turn into the wind after
clearing the ground with the tail rotor.
A confined area is an area where the flight of the heli­copter
is limited in some direction by terrain or the presence of
obstructions, natural or manmade. For example, a clearing
in the woods, a city street, a road, a building roof, etc., can
each be regarded as a confined area. The helicopter pilot has
added responsibilities when conducting operations from a
confined area that airplanes pilots do not. He or she assumes
the additional roles of the surveyor, engineer, and manager
when selecting an area to conduct operations. While airplane
pilots generally operate from known pre-surveyed and
improved landing areas, helicopter pilots fly into areas never
used before for helicopter operations. Generally, takeoffs and
landings should be made into the wind to obtain maximum
airspeed with minimum groundspeed. The pilot should begin
with as nearly accurate an altimeter setting as possible to
determine the altitude.
Common Errors
1.
Failing to adjust cyclic control to keep the heli­copter
from sliding down slope.
2.
Failing to maintain proper rpm.
3.
Holding excessive cyclic into the slope as the down
slope skid is raised.
4.
Failure to maintain heading, resulting in a turning or
pivoting motion.
5.
Turning the tail of the helicopter into the slope during
takeoff.
There are several things to consider when operating in
confined areas. One of the most important is maintaining
a clearance between the rotors and obstacles forming the
confined area. The tail rotor deserves special considera­tion
because, in some helicopters, it is not always visible from
the cabin. This not only applies while making the approach,
but also while hovering. Another consider­ation is that wires
are especially difficult to see; however, their supporting
devices, such as poles or towers, serve as an indication of
their presence and approximate height. If any wind is present,
expect some turbulence. [Figure 10-8]
WIND
Figure 10-8. If the wind velocity is 10 knots or greater, expect updrafts on the windward side and downdrafts on the lee side of obstacles.
Plan the approach with these factors in mind, but be ready to alter plans if the wind speed or direction changes.
10-9
Something else to consider is the availability of forced
landing areas during the planned approach. Think about
the possibility of flying from one alternate landing area to
another throughout the approach, while avoiding unfavorable
areas. Always leave a way out in case the landing cannot be
completed or a go-around is necessary.
During the high reconnaissance, the pilot needs to formulate
a takeoff plan as well. The heights of obstacles need to be
determined. It is not good practice to land in an area and
then determine that insufficient power exists to depart.
Generally, more power is required to take off than to land
so the takeoff criteria is most crucial. Fixing the departure
azimuth or heading on the compass is a good technique to
use. This ensures that the pilot is able to take off over the
preselected departure path when it is not visible while sitting
in the confined area.
Approach
A high reconnaissance should be completed before ini­tiating
the confined area approach. Start the approach phase using
the wind and speed to the best possible advantage. Keep in
mind areas suitable for forced land­ing. It may be necessary to
choose a crosswind approach that is over an open area, then
one directly into the wind that is over trees. If these conditions
exist, consider the possibility of making the initial phase of
the approach crosswind over the open area and then turn­ing
into the wind for the final portion of the approach.
Always operate the helicopter as close to its normal
capabilities as possible, taking into consideration the situation
at hand. In all confined area operations, with the exception
of the pinnacle operation, the angle of descent should be no
steeper than necessary to clear any barrier with the tail rotor
in the approach path and still land on the selected spot. The
angle of climb on takeoff should be normal, or not steeper
than necessary to clear any bar­rier. Clearing a barrier by a
few feet and maintaining normal operating rpm, with perhaps
a reserve of power, is better than clearing a barrier by a wide
mar­gin but with a dangerously low rpm and no power reserve.
Always make the landing to a specific point and not to some
general area. This point should be located well forward,
away from the approach end of the area. The more confined
the area is, the more essential it is that the helicopter land
precisely at a definite point. Keep this point in sight during
the entire final approach.
When flying a helicopter near obstacles, always consider
the tail rotor. A safe angle of descent over bar­riers must be
established to ensure tail rotor clearance of all obstructions.
After coming to a hover, avoid turning the tail into obstructions.
10-10
Takeoff
A confined area takeoff is considered an altitude over airspeed
maneuver where altitude gain is more important to airspeed
gain. Before takeoff, make a reconnaissance from the ground
or cockpit to determine the type of takeoff to be performed,
to determine the point from which the take­off should be
initiated to ensure the maximum amount of available area,
and finally, how to maneuver the helicopter best from the
landing point to the proposed take­off position.
If wind conditions and available area permit, the heli­
copter should be brought to a hover, turned around, and
hovered forward from the landing position to the take­off
position. Under certain conditions, sideward flight to the
takeoff position may be preferred, but rearward flight may
be necessary, stopping often while moving to check on the
location of obstacles relative to the tail rotor.
When planning the takeoff, consider the direction of the
wind, obstructions, and forced landing areas. To help fly up
and over an obstacle, form an imaginary line from a point
on the leading edge of the helicopter to the highest obstacle
to be cleared. Fly this line of ascent with enough power
to clear the obstacle by a safe distance. After clearing the
obstacle, maintain the power setting and accelerate to the
normal climb speed. Then, reduce power to the normal climb
power setting.
Common Errors
1.
Failure to perform, or improper performance of, a high
or low reconnaissance.
2.
Approach angle that is too steep or too shal­low for the
existing conditions.
3.
Failing to maintain proper rpm.
4.
Failure to consider emergency landing areas.
5.
Failure to select a specific landing spot.
6.
Failure to consider how wind and turbulence could
affect the approach.
7.
Improper takeoff and climb technique for exist­ing
conditions.
8.
Failure to maintain safe clearance distance from
obstructions.
Pinnacle and Ridgeline Operations
A pinnacle is an area from which the surface drops away
steeply on all sides. A ridgeline is a long area from which
the surface drops away steeply on one or two sides, such
as a bluff or precipice. The absence of obstacles does not
Approach and Landing
If there is a need to climb to a pinnacle or ridgeline, do it on
the upwind side, when practicable, to take advantage of any
updrafts. The approach flightpath should be paral­lel to the
ridgeline and into the wind as much as possi­ble. [Figure 10-9]
Figure 10-9. When flying an approach to a pinnacle or ridgeline,
avoid the areas where downdrafts are present, especially when
excess power is limited. If downdrafts are encountered, it may
become necessary to make an immediate turn away from the
pinnacle to avoid being forced into the rising terrain.
Load, altitude, wind conditions, and terrain features
determine the angle to use in the final part of an approach.
As a general rule, the greater the winds are, the steeper the
approach needs to be to avoid turbulent air and downdrafts.
Groundspeed during the approach is more difficult to judge
because visual references are farther away than during
approaches over trees or flat terrain. Pilots must continually
perceive the apparent rate of closure by observing the apparent
change in size of the landing zone features. Avoid the
appearance of an increasing rate of closure to the landing site.
The apparent rate of closure should be that of a brisk walk. If
a crosswind exists, remain clear of down-drafts on the leeward
or downwind side of the ridgeline. If the wind velocity makes
the crosswind landing hazardous, it may be possible to make
a low, coordinated turn into the wind just prior to terminating
the approach. When making an approach to a pinnacle, avoid
leeward turbulence and keep the helicopter within reach of a
forced landing area as long as possible.
On landing, take advantage of the long axis of the area when
wind conditions permit. Touchdown should be made in the
forward portion of the area. When approaching to land on
pinnacles, especially manmade areas such as rooftop pads,
the pilot should determine the personnel access pathway to
the helipad and ensure that the tail rotor is not allowed to
intrude into that walkway or zone. Parking or landing with the
tail rotor off the platform ensures personnel safety. Always
per­form a stability check prior to reducing rpm to ensure
the landing gear is on firm terrain that can safely support
the weight of the helicopter. Accomplish this by slowly
moving the cyclic and pedals while lowering the collective.
If movement is detected, reposition the aircraft.
Takeoff
A pinnacle takeoff is considered an airspeed over altitude
maneuver which can be made from the ground or from a
hover. Since pinnacles and ridgelines are generally higher
than the immediate surrounding terrain, gaining airspeed
on the takeoff is more important than gaining altitude. As
airspeed increases, the departure from the pinnacle is more
rapid and helicopter time in the “avoid” area of the height/
velocity decreases. [Figure 10-10] In addition to covering
unfavor­able terrain rapidly, a higher airspeed affords a more
favorable glide angle and thus contributes to the chances
of reaching a safe area in the event of a forced landing.
If a suitable forced landing area is not avail­able, a higher
airspeed also permits a more effective flare prior to making
an autorotative landing.
800
700
600
Height above ground (feet)
necessarily decrease the difficulty of pinnacle or ridgeline
operations. Updrafts, downdrafts, and turbulence, together
with unsuitable terrain in which to make a forced landing,
may still present extreme hazards.
500
400
300
Operation in shaded areas
must be avoided
200
8,500 lb gross weight
and below
100
0
0 10
20 30 40 50 60 70 80 90 100 110 120
Airspeed KIAS (knots)
Figure 10-10. Height/velocity chart.
10-11
On takeoff, as the helicopter moves out of ground effect,
maintain altitude and accelerate to normal climb airspeed.
When normal climb speed is attained, estab­lish a normal
climb attitude. Never dive the helicopter down the slope after
clearing the pinnacle.
Common Errors
1.
Failing to perform, or improper performance of, a high
or low reconnaissance.
2.
Flying the approach angle too steep or too shal­low for
the existing conditions.
3.
Failing to maintain proper rpm.
4.
Failing to consider emergency landing areas.
5.
Failing to consider how wind and turbulence could
affect the approach and takeoff.
6.
Failure to maintain pinnacle elevation after takeoff.
7.
Failure to maintain proper approach rate of closure.
8.
Failure to achieve climb airspeed in timely manner.
Chapter Summary
This chapter described advanced flight maneuvers such as
slope landings, confined area landings, and running takeoffs.
The correlation between helicopter power requirements, the
environment, and safety were also explained to familiarize
the pilot with how the helicopter reacts during different
maneuvers. Hazards associated with helicopter flight and
certain aerodynamic considerations were also discussed.
10-12
Chapter 11
Helicopter Emergencies
and Hazards
Introduction
Today, helicopters are quite reliable. However, emergencies
do occur, whether a result of mechanical failure or pilot
error, and should be anticipated. Regardless of the cause, the
recovery needs to be quick and precise. By having a thorough
knowledge of the helicopter and its systems, a pilot is able
to handle the situation more readily. Helicopter emergencies
and the proper recovery procedures should be discussed and,
when possible, practiced in flight. In addition, by knowing
the conditions that can lead to an emergency, many potential
accidents can be avoided.
11-1
Autorotation
In a helicopter, an autorotative descent is a power-off
maneuver in which the engine is disengaged from the main
rotor system and the rotor blades are driven solely by the
upward flow of air through the rotor. [Figure 11-1] In other
words, the engine is no longer supplying power to the main
rotor.
The most common reason for an autorotation is failure of the
engine or drive line, but autorotation may also be performed
in the event of a complete tail rotor failure, since there is
virtually no torque produced in an autorotation. In both
areas, maintenance has often been a contributing factor to the
failure. Engine failures are also caused by fuel contamination
or exhaustion as well resulting in a forced autorotation.
If the engine fails, the freewheeling unit automatically
disengages the engine from the main rotor allowing the
main rotor to rotate freely. Essentially, the freewheeling unit
disengages anytime the engine revolutions per minute (rpm)
is less than the rotor rpm.
At the instant of engine failure, the main rotor blades are
producing lift and thrust from their angle of attack (AOA)
and velocity. By lowering the collective pitch, which must be
done immediately in case of an engine failure, lift and drag
are reduced, and the helicopter begins an immediate descent,
thus producing an upward flow of air through the rotor
system. This upward flow of air through the rotor provides
sufficient thrust to maintain rotor rpm throughout the descent.
Since the tail rotor is driven by the main rotor transmission
during autorotation, heading control is maintained with the
antitorque pedals as in normal flight.
Several factors affect the rate of descent in autorotation:
density altitude, gross weight, rotor rpm, and airspeed. The
primary way to control the rate of descent is with airspeed.
Higher or lower airspeed is obtained with the cyclic pitch
control just as in normal powered flight. In theory, a pilot
has a choice in the angle of descent varying from a vertical
descent to maximum range, which is the minimum angle of
descent. Rate of descent is high at zero airspeed and decreases
to a minimum at approximately 50–60 knots, depending upon
the particular helicopter and the factors just mentioned. As
the airspeed increases beyond that which gives minimum rate
of descent, the rate of descent increases again.
When landing from an autorotation, the only energy available
to arrest the descent rate and ensure a soft landing is the
kinetic energy stored in the rotor blades. Tip weights can
greatly increase this stored energy. A greater amount of rotor
energy is required to stop a helicopter with a high rate of
descent than is required to stop a helicopter that is descending
more slowly. Therefore, autorotative descents at very low or
very high airspeeds are more critical than those performed
at the minimum rate of descent airspeed.
Each type of helicopter has a specific airspeed and rotor rpm
at which a power-off glide is most efficient. The specific
airspeed is somewhat different for each type of helicopter, but
certain factors affect all configurations in the same manner. In
general, rotor rpm maintained in the low green area gives more
distance in an autorotation. Higher weights may require more
collective pitch to control rotor rpm. Some helicopters need slight
adjustments to minimum rotor rpm settings for winter versus
summer conditions, and high altitude versus sea level flights. For
specific autorotation airspeeds and rotor rpm combinations for a
particular helicopter, refer to the Federal Aviation Administration
(FAA)-approved rotorcraft flight manual (RFM).
Autorotation
of
f
Di
re
cti
on
Direction of flight
lig
h
t
Normal Powered Flight
Figure 11-1. During an autorotation, the upward flow of relative wind permits the main rotor blades to rotate at their normal speed. In
effect, the blades are “gliding” in their rotational plane.
11-2
The specific airspeed and rotor rpm for autorotation is
established for each type of helicopter on the basis of
average weather, wind conditions, and normal loading.
When the helicopter is operated with heavy loads in high
density altitude or gusty wind conditions, best performance
is achieved from a slightly increased airspeed in the descent.
For autorotation at low density altitude and light loading,
best performance is achieved from a slight decrease in
normal airspeed. Following this general procedure of fitting
airspeed and rotor rpm to existing conditions, a pilot can
achieve approximately the same glide angle in any set of
circumstances and estimate the touchdown point.
Pilots should practice autorotations with varying airspeeds
between the minimum rate of descent to the maximum glide
angle airspeed. The decision to use the appropriate airspeed
for the conditions and availability of landing area must be
instinctive. The helicopter glide ratio is much less than that of
a fixed wing aircraft and takes some getting used to. The flare
to land at 55 KIAS will be significantly different than the flare
from 80 KIAS. Rotor rpm control is critical at these points
to ensure adequate rotor energy for cushioning the landing.
Straight-In Autorotation
A straight-in autorotation implies an autorotation from
altitude with no turns. Winds have a great effect on an
autorotation. Strong headwinds cause the glide angle to be
steeper due to the slower groundspeed. For example, if the
helicopter is maintaining 60 knots indicated airspeed and the
wind speed is 15 knots, then the groundspeed is 45 knots. The
angle of descent will be much steeper, although the rate of
descent remains the same. The speed at touchdown and the
resulting ground run depend on the groundspeed and amount
of deceleration. The greater the degree of deceleration, or
flare, and the longer it is held, the slower the touchdown speed
and the shorter the ground run. Caution must be exercised
at this point as the tail rotor will be the closest component
of the helicopter to the ground. If timing is not correct and a
landing attitude not set at the appropriate time, the tail rotor
may contact the ground causing a forward pitching moment
of the nose and possible damage to the helicopter.
A headwind is a contributing factor in accomplishing a slow
touchdown from an autorotative descent and reduces the
amount of deceleration required. The lower the speed desired
at touchdown is, the more accurate the timing and speed of
the flare must be, especially in helicopters with low-inertia
rotor systems. If too much collective pitch is applied too
early during the final stages of the autorotation, the kinetic
energy may be depleted, resulting in little or no cushioning
effect available. This could result in a hard landing with
corresponding damage to the helicopter. It is generally better
practice to accept more ground run than a hard landing with
minimal groundspeed. As proficiency increases, the amount
of ground run may be reduced.
Technique
Refer to Figure 11-2 (position 1). From level flight at
the appropriate airspeed (cruise or the manufacturer’s
recommended airspeed), 500–700 feet above ground level
(AGL), and heading into the wind, smoothly but firmly
lower the collective pitch control to the full down position,
maintaining rotor rpm in the green arc with collective. If
the collective is in the full down position, the rotor rpm is
then being controlled by the mechanical pitch stops. During
maintenance, the rotor stops must be set to allow minimum
autorotational rpm with a light loading. This means that some
collective pitch adjustment can be made if the air density or
helicopter loading changes. After entering an autorotation,
collective pitch must be adjusted to maintain the desired
rotor rpm.
1
2
3
4
5
Figure 11-2. Straight-in autorotation.
Coordinate the collective movement with proper antitorque
pedal for trim, and apply cyclic control to maintain proper
airspeed. Once the collective is fully lowered, decrease
throttle to ensure a clean split/separation of the needles. This
means that the rotor rpm is higher than the engine rpm and
a clear indication that the freewheeling unit has allowed the
engine to disconnect. After splitting the needles, readjust
the throttle to keep engine rpm above normal idling speed,
but not high enough to cause rejoining of the needles. The
manufacturer often recommends the proper rpm for that
particular helicopter.
At position 2, adjust attitude with cyclic control to obtain the
manufacturer’s recommended autorotation or best gliding
speed. Adjust collective pitch control, as necessary, to
maintain rotor rpm in the green arc. Aft cyclic movements
11-3
cause an increase in rotor rpm, which is then controlled by
a small increase in collective pitch control. Avoid a large
collective pitch increase, which results in a rapid decay of
rotor rpm, and leads to “chasing the rpm.” Avoid looking
straight down in front of the aircraft. Continually crosscheck
attitude, trim, rotor rpm, and airspeed.
At the altitude recommended by the manufacturer (position
3), begin the flare with aft cyclic control to reduce forward
airspeed and decrease the rate of descent. Maintain heading
with the antitorque pedals. During the flare maintain rotor rpm
in the green range. Care must be taken in the execution of the
flare so that the cyclic control is neither moved rearward so
abruptly that it causes the helicopter to climb nor moved so
slowly that it does not arrest the descent, which may allow
the helicopter to settle so rapidly that the tail rotor strikes
the ground. In most helicopters, the proper flare attitude is
noticeable by an apparent groundspeed of a slow run. When
forward motion decreases to the desired groundspeed, which
is usually the lowest possible speed (position 4), move the
cyclic control forward to place the helicopter in the proper
attitude for landing.
In many light helicopters, the student pilot can sit in the pilot
seat while the instructor pulls down on the helicopter’s tail
until the tail rotor guard or “stinger” touches the surface.
This action gives the student an idea of airframe attitude to
avoid, because a pilot should never allow ground contact
unless the helicopter is more nose low than that attitude.
Limiting the flare to that pitch attitude may result in slightly
faster touchdown speeds, but will eliminate the possibility
of tail rotor impact on level surfaces.
The landing gear height at this time should be approximately
3–15 feet AGL, depending on the altitude recommended by
the manufacturer. As the apparent groundspeed and altitude
decrease, the helicopter must be returned to a more level
attitude for touchdown by applying forward cyclic. Some
helicopters can be landed on the heels in a slightly nose high
attitude to help decrease the forward groundspeed whereas
others must land skids or landing gear level to equally spread
the landing loads to all of the landing gear. Extreme caution
should be used to avoid an excessive nose high and tail low
attitude below 10 feet. The helicopter must be close to the
landing attitude to keep the tail rotor from contacting the
surface.
At this point, if a full touchdown landing is to be made, allow
the helicopter to descend vertically (position 5). Increase
collective pitch, as necessary, to arrest the descent and
cushion the landing. This collective application uses some
of the potential energy in the rotor system to help slow the
descent rate of the helicopter. Additional antitorque pedal
11-4
is required to maintain heading as collective pitch is raised
due to the reduction in rotor rpm and the resulting reduced
effect of the tail rotor. Touch down in a level flight attitude.
Control response with increased pitch angles will be slightly
different than normal. With a decrease in main rotor rpm,
the antitorque authority is reduced, requiring larger control
inputs to maintain heading at touchdown.
Some helicopters have a canted tail stabilizer like the
Schweitzer 300. It is crucial that the student apply the
appropriate pedal input at all times during the autorotation.
If not the tailboom tends to swing to the right, which allows
the canted stabilizer to raise the tail. This can result in a
severe nose tuck which is quickly corrected with right pedal
application.
A power recovery can be made during training in lieu of a full
touchdown landing. Refer to the section on power recovery
for the correct technique. After the helicopter has come to a
complete stop after touchdown, lower the collective pitch to
the full-down position. Do not try to stop the forward ground
run with aft cyclic, as the main rotor blades can strike the
tail boom. Rather, by lowering the collective slightly during
the ground run, more weight is placed on the undercarriage,
slowing the helicopter.
One common error is holding the helicopter off the surface
versus cushioning the helicopter on to the surface during an
autorotation. Holding the helicopter in the air by using all of
the rotor rpm potential energy usually causes the helicopter to
have a hard landing, which results in the blades flexing down
and contacting the tail boom. The rotor rpm should be used
to cushion the helicopter on to the surface for a controlled,
smooth landing instead of allowing the helicopter to drop
the last few inches.
Common Errors
1.
Not understanding the importance of an immediate
entry into autorotation upon powerplant or driveline
failure.
2.
Failing to use sufficient antitorque pedal when power
is reduced.
3.
Lowering the nose too abruptly when power is
reduced, thus placing the helicopter in a dive.
4.
Failing to maintain proper rotor rpm during the
descent.
5.
Applying up-collective pitch at an excessive altitude,
resulting in a hard landing, loss of heading control,
and possible damage to the tail rotor and main rotor
blade stops.
6.
Failing to level the helicopter or achieve the
manufacturers preferred landing attitude.
7.
Failure to maintain ground track in the air and keeping
the landing gear aligned with the direction of travel
during touchdown and ground contact.
8.
Failure to minimize or eliminate lateral movement
during ground contact.
9.
Failure to go around if not within limits and specified
criteria for safe autorotation.
Autorotation With Turns
A turn, or a series of turns, can be made during an autorotation
in order to land into the wind or avoid obstacles. The turn is
usually made early so that the remainder of the autorotation
is the same as a straight-in autorotation. Making turns during
an autorotation generally uses cyclic control only. Use of
antitorque pedals to assist or increase the speed of the turn
causes loss of airspeed and downward pitching of the nose.
When an autorotation is initiated, sufficient antitorque pedal
pressure should be used to maintain the helicopter in trim
and prevent yawing. This pressure should not be changed
to assist the turn. If the helicopter is flown out of trim in
forward flight, the helicopter will be in either a slip or a skid
and airframe drag will be greatly increased which in turn
increases the rate of descent. Therefore, for the minimum
descent vertical speed, the trim ball should remain centered.
Use collective pitch control to manage rotor rpm. If rotor rpm
builds too high during an autorotation, raise the collective
sufficiently to decrease rpm back to the normal operating
range, then reduce the collective to maintain proper rotor rpm.
If the collective increase is held too long, the rotor rpm may
decay rapidly. The pilot must then lower the collective and
begin chasing the rotor rpm. If the rpm begins decreasing,
the pilot must again lower the collective. Always keep the
rotor rpm within the established range for the helicopter being
flown. During a turn, rotor rpm increases due to the increased
G loading, which induces a greater airflow through the rotor
system. The rpm builds rapidly and can easily exceed the
maximum limit if not controlled by use of collective. The
tighter the turn is and the heavier the gross weight is, the
higher the rpm is.
Cyclic input has a great effect on the rotor rpm. An aft cyclic
input loads the rotor, resulting in coning and an increase in
rotor rpm. A forward cyclic input unloads the rotor, resulting
in a decrease in rotor rpm. Therefore, it is prudent to attain
the proper pitch attitude needed to ensure that the desired
landing area can be reached as soon as possible, and to make
minor adjustments from there.
To initiate an autorotation in other than in a low hover, lower
the collective pitch control. This holds true whether performing
a practice autorotation or in the event of an in-flight engine
failure. This reduces the pitch of the main rotor blades and
allows them to continue turning at normal rpm. During practice
autorotations, maintain the rpm in the green arc with the throttle
while lowering collective. Once the collective is fully lowered,
reduce engine rpm by decreasing the throttle. This causes a
split of the engine and rotor rpm needles.
Technique
The most common types of autorotation are 90° and 180°
autorotations. For a 180° autorotation, establish the aircraft
on the downwind at recommended airspeed and 500–700
feet AGL, parallel to the touchdown area. In a no-wind or
headwind condition, establish the ground track approximately
200 feet away from the touchdown point. If a strong
crosswind exists, it is necessary to move the downwind leg
closer or farther out. When abeam the intended touchdown
point, smoothly but firmly lower the collective pitch control
to the full down position, maintaining rotor rpm in the green
arc with collective.
Coordinate the collective movement with proper antitorque
pedal for trim, and apply cyclic control to maintain proper
attitude. Once the collective is fully lowered, decrease throttle
to ensure a clean split/separation of the needles. After splitting
the needles, readjust the throttle to keep engine rpm above
normal idling speed, but not high enough to cause rejoining of
the needles. The manufacturer often recommends the proper
rpm for that particular helicopter. Crosscheck attitude, trim,
rotor rpm, and airspeed.
After the descent and airspeed are established, roll into
the turn. The turn should be approximately 180°, winds
may cause the actual turn to be more or less than 180°. For
training purposes, initially roll into a bank of a least 30°,
but no more than 50°– 60°. Continuously check airspeed,
rotor rpm, and trim throughout the turn. It is important to
maintain the proper airspeed and to keep the aircraft in trim.
Changes in the aircraft’s attitude and the angle of bank cause
a corresponding change in rotor rpm. Adjust the collective, as
necessary, in the turn to maintain rotor rpm in the green arc.
At the 90° point, check the progress of the turn by glancing
toward the landing area. Plan the second 90 degrees of turn
to roll out on the centerline. If the helicopter is too close,
decrease the bank angle; if too far out, increase the bank
angle. Adjusting the bank angle will change the G loading,
which in turn alters the airflow and results in rotor rpm
changes. Keep the helicopter in trim with antitorque pedals.
11-5
The turn should be completed and the helicopter aligned with
the intended touchdown area prior to passing through 100
feet AGL. If the collective pitch was temporarily increased
to control the rpm, it may need to be lowered on rollout to
prevent decay in rpm. Make an immediate power recovery
if the aircraft is not aligned with the touchdown point, and
if the rotor rpm and/or airspeed are not within proper limits.
Otherwise, complete the procedure as if it were a straight-in
autorotation.
Common Errors
1.
Failure to maintain trim during the turn (increases rate
of descent).
2.
Failure to maintain autorotation airspeed.
3.
Failure to hold proper pitch attitude for type helicopter
(too high or too low).
4.
Failure to have proper alignment with touchdown zone
by 100 feet AGL.
5.
Failure to maintain rotor rpm within limits during the
maneuver.
6.
Failure to go around if not within limits and specified
criteria for safe autorotation.
Practice Autorotation With a Power Recovery
A power recovery is used to terminate practice autorotations
at a point prior to actual touchdown. After the power
recovery, a landing can be made or a go-around initiated.
Technique
At approximately 3–15 feet landing gear height AGL,
depending upon the helicopter being used, begin to level the
helicopter with forward cyclic control. Avoid excessive nosehigh, tail-low attitude below 10 feet. Just prior to achieving
level attitude, with the nose still slightly up, coordinate
upward collective pitch control with an increase in the
throttle to join the needles at operating rpm. The throttle and
collective pitch must be coordinated properly.
If the throttle is increased too fast or too much, an engine
overspeed can occur; if throttle is increased too slowly or
too little in proportion to the increase in collective pitch, a
loss of rotor rpm results. Use sufficient collective pitch to
stop the descent, but keep in mind that the collective pitch
application must be gradual to allow for engine response.
Coordinate proper antitorque pedal pressure to maintain
heading. When a landing is to be made following the power
recovery, bring the helicopter to a hover at hovering altitude
and then descend to a landing.
When practicing autorotations with power recovery in nearly
all helicopters, the throttle or power levers should be at the
11-6
flight setting at the beginning of the flare. As the rotor system
begins to dissipate its energy, the engine is up to speed as
the needles join when the rotor decreases into the normal
flight rpm.
Helicopters that do not have the throttle control located on the
collective require some additional prudence. The autorotation
should be initiated with the power levers left in the “flight,”
or normal, position. If a full touchdown is to be practiced, it
is common technique to move the power levers to the idle
position once the landing area can safely be reached. In most
helicopters, the pilot is fully committed at that point to make
a power-off landing. However, it may be possible to make
a power recovery prior to passing through 100 feet AGL if
the powerplant can recover within that time period and the
instructor is very proficient. The pilot should comply with
the RFM instructions in all cases.
When practicing autorotations to a power recovery, the
differences between reciprocating engines and turbines
may be profound. The reciprocating powerplant generally
responds very quickly to power changes, especially power
increases. Some turbines have delay times depending on
the type of fuel control or governing system installed. Any
reciprocating engine needing turbocharged boost to develop
rated horse power may have significant delays to demands
for increased power, such as in the power recovery. Power
recovery in those helicopters with slower engine response
times must have the engines begin to develop enough power
to rejoin the needles by approximately 100 feet AGL.
If a go-around is to be made, the cyclic control should be
moved forward to resume forward flight. In transition from
a practice autorotation to a go-around, exercise caution to
avoid an altitude-airspeed combination that would place the
helicopter in an unsafe area of its height-velocity diagram.
This is one of the most difficult maneuvers to perform due to
the concentration needed when transitioning from powered
flight to autorotation and then back again to powered flight.
For helicopters equipped with the power control on the
collective, engine power must be brought from flight power
to idle power and then back to a flight power setting. A delay
during any of these transitions can seriously affect rotor rpm
placing the helicopter in a situation that cannot be recovered.
The cyclic must be adjusted to maintain the required
airspeed without power, and then used for the deceleration
flare, followed by the transition to level hovering flight.
Additionally, the cyclic must be adjusted to remove the
compensation for translating tendency. The tail rotor is
no longer needed to produce antitorque thrust until almost
maximum power is applied to the rotor system for hovering
flight, when the tail rotor must again compensate for the main
rotor torque, which also demands compensation for the tail
rotor thrust and translating tendency.
necessary to keep the helicopter from drifting to the left, to
compensate for the loss of tail rotor thrust. However, use
cyclic control, as required, to ensure a vertical descent and
a level attitude. Do not adjust the collective pitch on entry.
The pedals must be adjusted from a powered flight antitorque trim setting to the opposite trim setting to compensate
for transmission drag and any unneeded vertical fin thrust
countering the now nonexistent torque and then reset to
compensate for the high power required for hovering flight.
Helicopters with low inertia rotor systems settle immediately.
Keep a level attitude and ensure a vertical descent with
cyclic control while maintaining heading with the pedals.
Any lateral movement must be avoided to prevent dynamic
rollover. As rotor rpm decays, cyclic response decreases,
so compensation for winds will change, requiring more
cyclic input. At approximately 1 foot AGL, apply upward
collective pitch control, as necessary, to slow the descent
and cushion the landing without arresting the rate of descent
above the surface. Usually, the full amount of collective pitch
is required just as the landing gear touches the surface. As
upward collective pitch control is applied, the throttle must
be held in the idle detent position to prevent the engine from
re-engaging.
All of the above must be accomplished during the 23 seconds
of the autorotation and the tedious control inputs must be
made in the last 5 seconds of the maneuver.
Common Errors
1.
Initiating recovery too late, which requires a rapid
application of controls and results in overcontrolling.
2.
Failure to obtain and maintain a level attitude near the
surface.
3.
Failure to coordinate throttle and collective pitch
properly, which results in either an engine overspeed
or a loss of rotor rpm.
4.
Failure to coordinate proper antitorque pedal with the
increase in power.
5.
Late engine power engagement causing excessive
temperatures or torques, or rpm droop.
6.
Failure to go around if not within limits and specified
criteria for safe autorotation.
Power Failure in a Hover
Power failure in a hover, also called hovering autorotation, is
practiced so that a pilot can automatically make the correct
response when confronted with engine stoppage or certain
other emergencies while hovering. The techniques discussed
in this section are for helicopters with a counterclockwise
rotor system and an antitorque rotor.
Technique
To practice hovering autorotation, establish a normal
hovering altitude (approximately 2–3 feet) for the particular
helicopter being used, considering load and atmospheric
conditions. Keep the helicopter headed into the wind and
hold maximum allowable rpm.
To simulate a power failure, firmly roll the throttle to the
engine idle position. This disengages the driving force of the
engine from the rotor, thus eliminating torque effect. As the
throttle is closed, apply proper antitorque pedal to maintain
heading. Usually, a slight amount of right cyclic control is
Helicopters with high inertia rotor systems settle more slowly
after the throttle is closed. When the helicopter has settled
to approximately 1 foot AGL, apply upward collective pitch
control while holding the throttle in the idle detent position
to slow the descent and cushion the landing. The timing of
collective pitch control application and the rate at which it is
applied depend upon the particular helicopter being used, its
gross weight, and the existing atmospheric conditions. Cyclic
control is used to maintain a level attitude and to ensure a
vertical descent. Maintain heading with antitorque pedals.
When the weight of the helicopter is entirely resting on
the landing gear, cease application of upward collective.
When the helicopter has come to a complete stop, lower the
collective pitch to the full-down position.
The timing of the collective pitch is a most important
consideration. If it is applied too soon, the remaining rpm
may not be sufficient to make a soft landing. On the other
hand, if collective pitch control is applied too late, surface
contact may be made before sufficient blade pitch is available
to cushion the landing. The collective must not be used to
hold the helicopter off the surface, causing a blade stall. Low
rotor rpm and ensuing blade stall can result in a total loss
of rotor lift allowing the helicopter to fall to the surface and
possibly resulting in blade strikes to the tail boom and other
airframe damage such as landing gear damage, transmission
mount deformation, and fuselage cracking.
Common Errors
1.
Failure to use sufficient proper antitorque pedal when
power is reduced.
11-7
2.
Failure to stop all sideward or backward movement
prior to touchdown.
3.
Failure to apply up-collective pitch properly, resulting
in a hard touchdown.
4.
Failure to touch down in a level attitude.
5.
Failure to roll the throttle completely to idle.
6.
Failure to hover at a safe altitude for the helicopter
type, atmospheric conditions, and the level of training/
proficiency of the pilot.
7.
Failure to go around if not within limits and specified
criteria for safe autorotation.
Height/Velocity Diagram
The height/velocity diagram or H/V curve is a graph charting
the safe/unsafe flight profiles relevant to a specific helicopter.
As operation outside the safe area of the chart can be fatal
in the event of a power or driveline failure, it is sometimes
referred to as the dead man’s curve by helicopter pilots. By
carefully studying the height/velocity diagram, a pilot is
able to avoid the combinations of altitude and airspeed that
may not allow sufficient time or altitude to enter a stabilized
autorotative descent. A pilot may want to refer to this diagram
during the remainder of the discussion on the height/velocity
diagram. [Figure 11-3]
500
450
Avoid operation in shaded areas
400
Height above surface (feet)
Smooth hard surface
300
250
A
150
100
50
0
B
0
10
20
30
40
50
60
70
80
Indicated airspeed (knots)
(corrected for instrument error)
Figure 11-3. Height/velocity diagram.
11-8
The portion in the upper left of this diagram demonstrates
a flight profile that probably does not allow the pilot to
complete an autorotation successfully, primarily due to
having insufficient airspeed to enter an autorotative profile
in time to avoid a crash. The shaded area on the lower right
is dangerous due to the airspeed and proximity to the ground
resulting in dramatically reduced reaction time for the pilot in
the case of mechanical failure, or other in-flight emergencies.
This shaded area at the lower right is not portrayed in H/V
curves for multi-engine helicopters capable of safely hovering
and flying with a single engine failure.
The following examples further illustrate the relevance of
the H/V curve to a single-engine helicopter.
At low heights with low airspeed, such as a hover taxi, the
pilot can simply use the potential energy from the rotor
system to cushion the landing with collective, converting
rotational inertia to lift. The aircraft is in a safe part of the
H/V curve. At the extreme end of the scale (e.g., a threefoot hover taxi at walking pace) even a complete failure to
recognize the power loss resulting in an uncushioned landing
would probably be survivable.
As the airspeed increases without an increase in height,
there comes a point at which the pilot’s reaction time would
be insufficient to react with a flare in time to prevent a high
speed, and thus probably fatal, ground impact. Another thing
to consider is the length of the tailboom and the response
time of the helicopter flight controls at slow airspeeds and
low altitudes. Even small increases in height give the pilot
much greater time to react; therefore, the bottom right part
of the H/V curve is usually a shallow gradient. If airspeed is
above ideal autorotation speed, the pilot’s instinct is usually
to flare to convert speed to height and increase rotor rpm
through coning, which also immediately gets them out of
the dead man’s curve.
350
200
In the simplest explanation, the H/V curve is a diagram in
which the shaded areas should be avoided, as the pilot may be
unable to complete an autorotation landing without damage.
The H/V curve usually contains a takeoff profile, where the
diagram can be traversed from 0 height and 0 speed to cruise,
without entering the shaded areas or with minimum exposure
to shaded areas.
90 100
Conversely, an increase in height without a corresponding
increase in airspeed puts the aircraft above a survivable
uncushioned impact height, and eventually above a height
where rotor inertia can be converted to sufficient lift to enable
a survivable landing. This occurs abruptly with airspeeds
much below the ideal autorotative speed (typically 40–80
knots). The pilot must have enough time to accelerate to
autorotation speed in order to autorotate successfully; this
directly relates to a requirement for height. Above a certain
height the pilot can achieve autorotation speed even from a
0 knot start, thus putting high OGE hovers outside the curve.
The typical safe takeoff profile involves initiation of forward
flight from a 2–3 feet landing gear height, only gaining
altitude as the helicopter accelerates through translational lift
and airspeed approaches a safe autorotative speed. At this
point, some of the increased thrust available may be used to
attain safe climb airspeed and will keep the helicopter out of
the shaded or hatched areas of the H/V diagram. Although
helicopters are not restricted from conducting maneuvers
that will place them in the shaded area of the H/V chart, it
is important for pilots to understand that operation in those
shaded areas exposes pilot, aircraft, and passengers to a
certain hazard should the engine or driveline malfunction.
The pilot should always evaluate the risk of the maneuver
versus the operational value.
The Effect of Weight Versus Density Altitude
The height/velocity diagram [Figure 11-3] depicts altitude
and airspeed situations from which a successful autorotation
can be made. The time required, and therefore, altitude
necessary to attain a steady state autorotative descent, is
dependent on the weight of the helicopter and the density
altitude. For this reason, the H/V diagram is valid only when
the helicopter is operated in accordance with the gross weight
versus density altitude chart. If published, this chart is found
in the RFM for the particular helicopter. [Figure 11-4] The
gross weight versus density altitude chart is not intended to
Density altitude (thousands of feet)
7
6
B
provide a restriction to gross weight, but to be an advisory of
the autorotative capability of the helicopter during takeoff and
climb. A pilot must realize, however, that at gross weights
above those recommended by the gross weight versus density
altitude chart, the values are unknown.
Assuming a density altitude of 5,500 feet, the height/velocity
diagram in Figure 11-3 would be valid up to a gross weight
of approximately 1,700 pounds. This is found by entering
the graph in Figure 11-4 at a density altitude of 5,500 feet
(point A), then moving horizontally to the solid line (point
B). Moving vertically to the bottom of the graph (point C),
with the existing density altitude, the maximum gross weight
under which the height/velocity diagram is applicable is
1,700 pounds.
Charts and diagrams for helicopters set out in Title 14 of the
Code of Federal Regulations (14 CFR) Part 27, Airworthiness
Standards: Normal Category Rotorcraft, are advisory in nature
and not regulatory. However, these charts do establish the safe
parameters for operation. It is important to remember these
guidelines establish the tested capabilities of the helicopter.
Unless the pilot in command (PIC) is a certificated test pilot,
operating a helicopter beyond its established capabilities can
be considered careless and reckless operation, especially if
this action results is death or injury.
Common Errors
1.
Performing hovers higher than performed during
training for hovering autorotations and practiced
proficiency.
2.
Excessively nose-low takeoffs. The forward landing
gear would impact before the pilot could assume a
landing attitude.
3.
Adding too much power for takeoff.
4.
Not maintaining landing gear aligned with takeoff
path until transitioning to a crab heading to account
for winds.
A
5
Settling With Power (Vortex Ring State)
4
Vortex ring state describes an aerodynamic condition in
which a helicopter may be in a vertical descent with 20
percent up to maximum power applied, and little or no climb
performance. The term “settling with power” comes from
the fact that the helicopter keeps settling even though full
engine power is applied.
3
1,500
C
1,600
1,700
1,800
1,900
Gross weight (pounds)
Figure 11-4. Gross weight versus density altitude.
2,000
In a normal out-of-ground-effect (OGE) hover, the helicopter
is able to remain stationary by propelling a large mass of air
down through the main rotor. Some of the air is recirculated
near the tips of the blades, curling up from the bottom of the
11-9
rotor system and rejoining the air entering the rotor from
the top. This phenomenon is common to all airfoils and is
known as tip vortices. Tip vortices generate drag and degrade
airfoil efficiency. As long as the tip vortices are small, their
only effect is a small loss in rotor efficiency. However, when
the helicopter begins to descend vertically, it settles into its
own downwash, which greatly enlarges the tip vortices. In
this vortex ring state, most of the power developed by the
engine is wasted in circulating the air in a doughnut pattern
around the rotor.
The following combination of conditions is likely to cause
settling in a vortex ring state in any helicopter:
In addition, the helicopter may descend at a rate that exceeds
the normal downward induced-flow rate of the inner blade
sections. As a result, the airflow of the inner blade sections is
upward relative to the disk. This produces a secondary vortex
ring in addition to the normal tip vortices. The secondary
vortex ring is generated about the point on the blade where the
airflow changes from up to down. The result is an unsteady
turbulent flow over a large area of the disk. Rotor efficiency
is lost even though power is still being supplied from the
engine. [Figure 11-5]
Some of the situations that are conducive to a settling with
power condition are: any hover above ground effect altitude,
specifically attempting to hover OGE at altitudes above the
hovering ceiling of the helicopter, attempting to hover OGE
without maintaining precise altitude control, pinnacle or
rooftop helipads when the wind is not aligned with the landing
direction, and downwind and steep power approaches in
which airspeed is permitted to drop below 10 knots depending
on the type of helicopter.
1.
A vertical or nearly vertical descent of at least 300
fpm. (Actual critical rate depends on the gross weight,
rpm, density altitude, and other pertinent factors.)
2.
The rotor system must be using some of the available
engine power (20–100 percent).
3.
The horizontal velocity must be slower than effective
translational lift.
When recovering from a settling with power condition,
the pilot tends first to try to stop the descent by increasing
collective pitch. However, this only results in increasing
the stalled area of the rotor, thereby increasing the rate of
descent. Since inboard portions of the blades are stalled,
cyclic control may be limited. Recovery is accomplished
by increasing airspeed, and/or partially lowering collective
pitch. In many helicopters, lateral cyclic combined with
lateral tailrotor thrust will produce the quickest exit from the
hazard assuming that there are no barriers in that direction.
In a fully developed vortex ring state, the only recovery may
be to enter autorotation to break the vortex ring state.
Tandem rotor helicopters should maneuver laterally to
achieve clean air in both rotors at the same time.
Figure 11-5. Vortex ring state.
A fully developed vortex ring state is characterized by an
unstable condition in which the helicopter experiences
uncommanded pitch and roll oscillations, has little or no
collective authority, and achieves a descent rate that may
approach 6,000 feet per minute (fpm) if allowed to develop.
A vortex ring state may be entered during any maneuver
that places the main rotor in a condition of descending in a
column of disturbed air and low forward airspeed. Airspeeds
that are below translational lift airspeeds are within this
region of susceptibility to settling with power aerodynamics.
This condition is sometimes seen during quick-stop type
maneuvers or during recovery from autorotation.
11-10
For settling with power demonstrations and training in
recognition of vortex ring state conditions, all maneuvers
should be performed at an altitude of 2000–3000 feet AGL
to allow sufficient altitude for entry and recovery.
To enter the maneuver, come to an OGE hover, maintaining
little or no airspeed (any direction), decrease collective
to begin a vertical descent, and as the turbulence begins,
increase collective. Then allow the sink rate to increase to 300
fpm or more as the attitude is adjusted to obtain airspeed of
less than 10 knots. When the aircraft begins to shudder, the
application of additional up collective increases the vibration
and sink rate. As the power is increased, the rate of sink of
the aircraft in the column of air will increase.
If altitude is sufficient, some time can be spent in the
vortices, to enable the pilot to develop a healthy knowledge
of the maneuver. However, helicopter pilots would normally
initiate recovery at the first indication of settling with power.
Recovery should be initiated at the first sign of vortex ring
state by applying forward cyclic to increase airspeed and/ or
simultaneously reducing collective. The recovery is complete
when the aircraft passes through effective translational lift
and a normal climb is established.
Common Errors
1.
Too much lateral speed for entry into settling with
power.
2.
Excessive decrease of collective pitch.
Retreating Blade Stall
In forward flight, the relative airflow through the main rotor
disk is different on the advancing and retreating side. The
relative airflow over the advancing side is higher due to the
forward speed of the helicopter, while the relative airflow on
the retreating side is lower. This dissymmetry of lift increases
as forward speed increases.
To generate the same amount of lift across the rotor disk,
the advancing blade flaps up while the retreating blade flaps
down. This causes the AOA to decrease on the advancing
blade, which reduces lift, and increase on the retreating blade,
which increases lift. At some point as the forward speed
increases, the low blade speed on the retreating blade, and
its high AOA cause a stall and loss of lift.
Retreating blade stall is a major factor in limiting a
helicopter’s never-exceed speed (VNE) and its development
can be felt by a low frequency vibration, pitching up of the
nose, and a roll in the direction of the retreating blade. High
weight, low rotor rpm, high density altitude, turbulence and/
or steep, abrupt turns are all conducive to retreating blade
stall at high forward airspeeds. As altitude is increased, higher
blade angles are required to maintain lift at a given airspeed.
Thus, retreating blade stall is encountered at a lower forward
airspeed at altitude. Most manufacturers publish charts and
graphs showing a VNE decrease with altitude.
When recovering from a retreating blade stall condition,
moving the cyclic aft only worsens the stall as aft cyclic
produces a flare effect, thus increasing the AOA. Pushing
forward on the cyclic also deepens the stall as the AOA on the
retreating blade is increased. Correct recovery from retreating
blade stall requires the collective to be lowered first, which
reduces blade angles and thus AOA. Aft cyclic can then be
used to slow the helicopter.
Common Errors
1.
Failure to recognize the combination of contributing
factors leading to retreating blade stall.
2.
Failure to compute VNE limits for altitudes to be flown.
Ground Resonance
Helicopters with articulating rotors (usually designs with
three or more main rotor blades) are subject to ground
resonance, a destructive vibration phenomenon that occurs
at certain rotor speeds when the helicopter is on the ground.
Ground resonance is a mechanical design issue that results
from the helicopter’s airframe having a natural frequency that
can be intensified by an out-of-balance rotor. The unbalanced
rotor system vibrates at the same frequency or multiple of the
airframe’s resonant frequency and the harmonic oscillation
increases because the engine is adding power to the system,
increasing the magnitude (or amplitude) of the vibrations
until the structure or structures fail. This condition can cause
a helicopter to self-destruct in a matter of seconds.
Hard contact with the ground on one corner (and usually
with wheel-type landing gear) can send a shockwave to the
main rotor head, resulting in the blades of a three-blade rotor
system moving from their normal 120° relationship to each
other. This movement occurs along the drag hinge and could
result in something like 122°, 122°, and 116° between blades.
[Figure 11-6] When one of the other landing gear strikes the
surface, the unbalanced condition could be further aggravated.
If the rpm is low, the only corrective action to stop ground
resonance is to close the throttle immediately and fully lower
the collective to place the blades in low pitch. If the rpm is in
the normal operating range, fly the helicopter off the ground,
122°
12
2°
116°
Figure 11-6. Ground resonance.
11-11
and allow the blades to rephase themselves automatically.
Then, make a normal touchdown. If a pilot lifts off and allows
the helicopter to firmly re-contact the surface before the
blades are realigned, a second shock could move the blades
again and aggravate the already unbalanced condition. This
could lead to a violent, uncontrollable oscillation.
force that rolls the helicopter over. When limited rotor blade
movement is coupled with the fact that most of a helicopter’s
weight is high in the airframe, another element of risk is added
to an already slightly unstable center of gravity. Pilots must
remember that in order to remove thrust, the collective must
be lowered as this is the only recovery technique available.
This situation does not occur in rigid or semi-rigid rotor
systems because there is no drag hinge. In addition, skid-type
landing gear is not as prone to ground resonance as wheeltype landing gear since the rubber tires are not present and
change the rebound characteristics.
Critical Conditions
Certain conditions reduce the critical rollover angle, thus
increasing the possibility for dynamic rollover and reducing
the chance for recovery. The rate of rolling motion is also
a consideration because, as the roll rate increases, there is
a reduction of the critical rollover angle at which recovery
is still possible. Other critical conditions include operating
at high gross weights with thrust (lift) approximately equal
to the weight.
Dynamic Rollover
A helicopter is susceptible to a lateral rolling tendency, called
dynamic rollover, when the helicopter is in contact with the
surface during takeoffs or landings. For dynamic rollover to
occur, some factor must first cause the helicopter to roll or
pivot around a skid or landing gear wheel, until its critical
rollover angle is reached. (5–8° depending on helicopter,
winds, and loading) Then, beyond this point, main rotor
thrust continues the roll and recovery is impossible. After this
angle is achieved, the cyclic does not have sufficient range
of control to eliminate the thrust component and convert it to
lift. If the critical rollover angle is exceeded, the helicopter
rolls on its side regardless of the cyclic corrections made.
Refer to Figure 11-7. The following conditions are most
critical for helicopters with counterclockwise rotor rotation:
1.
Right side skid or landing wheel down, since
translating tendency adds to the rollover force.
2.
Right lateral center of gravity (CG).
3.
Crosswinds from the left.
4.
Left yaw inputs.
Dynamic rollover begins when the helicopter starts to pivot
laterally around its skid or wheel. This can occur for a variety
of reasons, including the failure to remove a tie down or
skid-securing device, or if the skid or wheel contacts a fixed
object while hovering sideward, or if the gear is stuck in
ice, soft asphalt, or mud. Dynamic rollover may also occur
if you use an improper landing or takeoff technique or while
performing slope operations. Whatever the cause, if the gear
or skid becomes a pivot point, dynamic rollover is possible
if not using the proper corrective technique.
Once started, dynamic rollover cannot be stopped by
application of opposite cyclic control alone. For example,
the right skid contacts an object and becomes the pivot
point while the helicopter starts rolling to the right. Even
with full left cyclic applied, the main rotor thrust vector and
its moment follows the aircraft as it continues rolling to the
right. Quickly reducing collective pitch is the most effective
way to stop dynamic rollover from developing. Dynamic
rollover can occur with any type of landing gear and all types
of rotor systems.
It is important to remember rotor blades have a limited range
of movement. If the tilt or roll of the helicopter exceeds that
range (5–8°), the controls (cyclic) can no longer command a
vertical lift component and the thrust or lift becomes a lateral
11-12
Main rotor thrust
hrust
otor t
Tail r
yclic
utral c
ne ne
pla
ip-path
T
ft cyclic
ane full le
Tip-path pl
Crosswind
CG
Bank
angle
Pivot point
Weight
Figure 11-7. Forces acting on a helicopter with right skid on the
ground.
For helicopters with clockwise rotor rotation, the opposite
conditions would be true.
Cyclic Trim
When maneuvering with one skid or wheel on the ground,
care must be taken to keep the helicopter cyclic control
carefully adjusted. For example, if a slow takeoff is attempted
and the cyclic is not positioned and adjusted to account for
translating tendency, the critical recovery angle may be
exceeded in less than two seconds. Control can be maintained
if the pilot maintains proper cyclic position, and does not
allow the helicopter’s roll and pitch rates to become too
great. Fly the helicopter into the air smoothly while keeping
movements of pitch, roll, and yaw small; do not allow any
abrupt cyclic pressures.
Full opposite cyclic limit
to prevent rolling motion
t
r thrus
Tail roto
Area
of crit
ical ro
Slope
llover
Horizontal
Normal Takeoffs and Landings
Dynamic rollover is possible even during normal takeoffs
and landings on relatively level ground, if one wheel or
skid is on the ground and thrust (lift) is approximately equal
to the weight of the helicopter. If the takeoff or landing is
not performed properly, a roll rate could develop around
the wheel or skid that is on the ground. When taking off or
landing, perform the maneuver smoothly and carefully adjust
the cyclic so that no pitch or roll movement rates build up,
especially the roll rate. If the bank angle starts to increase to
an angle of approximately 5–8°, and full corrective cyclic
does not reduce the angle, the collective should be reduced
to diminish the unstable rolling condition. Excessive bank
angles can also be caused by landing gear caught in a tie
down strap, or a tie down strap still attached to one side of
the helicopter. Lateral loading imbalance (usually outside
published limits) is another contributing factor.
Slope Takeoffs and Landings
During slope operations, excessive application of cyclic
control into the slope, together with excessive collective pitch
control, can result in the downslope skid or landing wheel
rising sufficiently to exceed lateral cyclic control limits, and
an upslope rolling motion can occur. [Figure 11-8]
When performing slope takeoff and landing maneuvers,
follow the published procedures and keep the roll rates
small. Slowly raise the downslope skid or wheel to bring the
helicopter level, and then lift off. During landing, first touch
down on the upslope skid or wheel, then slowly lower the
downslope skid or wheel using combined movements of cyclic
and collective. If the helicopter rolls approximately 5–8° to the
upslope side, decrease collective to correct the bank angle and
return to level attitude, then start the landing procedure again.
Use of Collective
The collective is more effective in controlling the rolling
motion than lateral cyclic, because it reduces the main rotor
thrust (lift). A smooth, moderate collective reduction, at a
rate of less than approximately full up to full down in two
Figure 11-8. Upslope rolling motion.
seconds, may be adequate to stop the rolling motion. Take
care, however, not to dump collective at an excessively
high rate, as this may cause a main rotor blade to strike the
fuselage. Additionally, if the helicopter is on a slope and the
roll starts toward the upslope side, reducing collective too fast
may create a high roll rate in the opposite direction. When
the upslope skid or wheel hits the ground, the dynamics of
the motion can cause the helicopter to bounce off the upslope
skid or wheel, and the inertia can cause the helicopter to roll
about the downslope ground contact point and over on its
side. [Figure 11-9]
Full opposite cyclic limit
to prevent rolling motion
t
r thrus
Tail roto
ao
Are
er
llov
al ro
tic
f cri
Slope
Horizontal
Figure 11-9. Downslope rolling motion.
Under normal conditions, the collective should not be pulled
suddenly to get airborne because a large and abrupt rolling
moment in the opposite direction could occur. Excessive
application of collective can result in the upslope skid or
wheel rising sufficiently to exceed lateral cyclic control
limits. This movement may be uncontrollable. If the
11-13
helicopter develops a roll rate with one skid or wheel on the
ground, the helicopter can roll over on its side.
Precautions
To help avoid dynamic rollover:
1.
Always practice hovering autorotations into the wind,
and be wary when the wind is gusty or greater than 10
knots.
2.
Use extreme caution when hovering close to fences,
sprinklers, bushes, runway/taxi lights, tiedown cables,
deck nets, or other obstacles that could catch a skid
or wheel. Aircraft parked on hot asphalt over night
might find the landing gear sunk in and stuck as the
ramp cooled during the evening.
3.
Always use a two-step lift-off. Pull in just enough
collective pitch control to be light on the skids or
landing wheels and feel for equilibrium, then gently
lift the helicopter into the air.
4.
Hover high enough to have adequate skid or landing
wheel clearance with any obstacles when practicing
hovering maneuvers close to the ground, especially
when practicing sideways or rearward flight.
5.
Remember that when the wind is coming from
the upslope direction, less lateral cyclic control is
available.
6.
Avoid tailwind conditions when conducting slope
operations.
7.
Remember that less lateral cyclic control is available
due to the translating tendency of the tail rotor when
the left skid or landing wheel is upslope. (This is true
for counterclockwise rotor systems.)
8.
Keep in mind that the lateral cyclic requirement
changes when passengers or cargo are loaded or
unloaded.
9.
Be aware that if the helicopter utilizes interconnecting
fuel lines that allow fuel to automatically transfer from
one side of the helicopter to the other, the gravitational
flow of fuel to the downslope tank could change the
CG, resulting in a different amount of cyclic control
application to obtain the same lateral result.
10. Do not allow the cyclic limits to be reached. If the
cyclic control limit is reached, further lowering of the
collective may cause mast bumping. If this occurs,
return to a hover and select a landing point with a
lesser degree of slope.
11. During a takeoff from a slope, begin by leveling the
main rotor disk with the horizon or very slightly into
the slope to ensure vertical lift and only enough lateral
thrust to prevent sliding on the slope. If the upslope
11-14
skid or wheel starts to leave the ground before the
downslope skid or wheel, smoothly and gently lower
the collective and check to see if the downslope skid or
wheel is caught on something. Under these conditions,
vertical ascent is the only acceptable method of lift-off.
12. Be aware that dynamic rollover can be experienced
during flight operations on a floating platform if the
platform is pitching/rolling while attempting to land
or takeoff. Generally, the pilot operating on floating
platforms (barges, ships, etc.) observes a cycle of
seven during which the waves increase and then
decrease to a minimum. It is that time of minimum
wave motion that the pilot needs to use for the moment
of landing or takeoff on floating platforms. Pilots
operating from floating platforms should also exercise
great caution concerning cranes, masts, nearby boats
(tugs) and nets.
Low-G Conditions and Mast Bumping
Low acceleration of gravity (low-G or weightless) maneuvers
create specific hazards for helicopters, especially those with
semirigid main rotor systems because helicopters are primarily
designed to be suspended from the main rotor in normal flight
with only small variations for positive G load maneuvers.
Since a helicopter low-G maneuver departs from normal
flight conditions, it may allow the airframe to exceed the
manufacturer’s design criteria. A low-G condition could have
disastrous results, the best way to prevent it from happening is
to avoid the conditions in which it might occur.
Low-G conditions are not about the loss of thrust, rather the
imbalance of forces. Helicopters are mostly designed to have
weight (gravity pulling down to the earth) and lift opposing
that force of gravity. Low-G maneuvers occur when this
balance is disturbed. An example of this would be placing the
helicopter into a very steep dive. At the moment of pushover,
the lift and thrust of the rotor is forward, whereas gravity
is now vertical or straight down. Since the lift vector is no
longer vertical and opposing the gravity (or weight) vector,
the fuselage is now affected by the tail rotor thrust below the
plane of the main rotor. This tail rotor thrust moment tends to
make the helicopter fuselage tilt to the left. Pilots then apply
right cyclic inputs to try to correct for the left. Since the main
rotor system does not fully support the fuselage at this point,
the fuselage continues to roll and the pilot applies more right
cyclic until the rotor system strikes the mast (mast bumping),
often ending with unnecessary fatal results. In mast bumping,
the rotor blade exceeds its flapping limits, causing the main
rotor hub to “bump” into the rotor shaft. [Figure 11-10] The
main rotor hub’s contact with the mast usually becomes more
violent with each successive flapping motion. This creates a
greater flapping displacement and leads to structural failure of
point, airflow will provide no any lift or driving force for
the system, and the result is disastrous.
Even though there is a safety factor built into most
helicopters, any time rotor rpm falls below the green arc
and there is power, simultaneously add throttle and lower
the collective. If in forward flight, gently applying aft cyclic
causes more air flow through the rotor system and helps
increase rotor rpm. If without power, immediately lower the
collective and apply aft cyclic.
Recovery From Low Rotor RPM
Figure 11-10. Result of improper corrective action in a low-G
condition.
the rotor shaft. Since the mast is hollow, the structural failure
manifests itself either as shaft failure with complete separation
of the main rotor system from the helicopter or a severely
damaged rotor mast.
In situations like the one described above, the helicopter pilot
should first apply aft cyclic to bring the vectors into balance,
with lift up and gravity down. Since helicopter blades carry
the helicopter and have limited motion attachment, care must
be given to those attachment limits. Helicopter pilots should
always adhere to the maneuvering limitations stated in the
RFM. There may be more than one reason or design criteria
which limits the helicopters flight envelope. Heed all of the
manufacturer’s limitations and advisory data. Failure to do so
could lead to dire, unintended consequences.
Low Rotor RPM and Blade Stall
As mentioned earlier, low rotor rpm during an autorotation
might result in a less than successful maneuver. However,
if rotor rpm decays to the point at which all the rotor blades
stall, the result is usually fatal, especially when it occurs at
altitude. It can occur in a number of ways, such as simply
rolling the throttle the wrong way, pulling more collective
pitch than power available, or when operating at a high
density altitude.
When the rotor rpm decreases, the blades produce less lift
so the pilot feels it necessary to increase collective pitch to
stop the descent or increase the climb. As the pitch increases,
drag increases, which requires more power to keep the
blades turning at the proper rpm. When power is no longer
available to maintain rpm and, therefore, lift, the helicopter
begins to descend. This changes the relative wind and further
increases the AOA. At some point, the blades stall unless
rpm is restored. As main rotor RPM decays, centrifugal
force continues to lessen until the lift force overcomes the
centrifugal forces and folds or breaks the blades. At this
Under certain conditions of high weight, high temperature,
or high density altitude, a pilot may get into a low rotor rpm
situation. Although the pilot is using maximum throttle, the
rotor rpm is low and the lifting power of the main rotor blades
is greatly diminished. In this situation, the main rotor blades
have an AOA that has created so much drag that engine power
is not sufficient to maintain or attain normal operating rpm.
When rotor rpm begins to decrease, it is essential to recover
and maintain it.
As soon as a low rotor rpm condition is detected, apply
additional throttle if it is available. If there is no throttle
available, lower the collective. The amount the collective
can be lowered depends on altitude. Rotor rpm is life! If
the engine rpm is too low, it cannot produce its rated power
for the conditions because power generation is defined at a
qualified rpm value. An rpm that is too low equals low power.
Main rotor rpm must be maintained.
When operating at altitude, the collective may need to be
lowered only once to regain rotor speed. If power is available,
throttle can be added and the collective raised. Once
helicopter rotor blades cone excessively due to low rotor rpm,
return the helicopter to the surface to allow the main rotor
rpm to recover. Maintain precise landing gear alignment with
the direction of travel in case a landing is necessary. Low
inertia rotor systems can become unrecoverable in 2 seconds
or less if the rpm is not regained immediately.
Since the tail rotor is geared to the main rotor, low main rotor
rpm may prevent the tail rotor from producing enough thrust
to maintain directional control. If pedal control is lost and the
altitude is low enough that a landing can be accomplished
before the turning rate increases dangerously, slowly decrease
collective pitch, maintain a level attitude with cyclic control,
and land.
11-15
System Malfunctions
The reliability and dependability record of modern helicopters
is very impressive. By following the manufacturer’s
recommendations regarding operating limits and procedures
and periodic maintenance and inspections, most systems and
equipment failures can be eliminated. Most malfunctions or
failures can be traced to some error on the part of the pilot;
therefore, most emergencies can be averted before they
happen. An actual emergency is a rare occurrence.
Antitorque System Failure
Antitorque failure usually falls into one of two categories.
One is failure of the power drive portion of the tail rotor
system resulting in a complete loss of antitorque. The other
category covers mechanical control failures prohibiting
the pilot from changing or controlling tail rotor thrust even
though the tail rotor may still be providing antitorque thrust.
Tail rotor drive system failures include driveshaft failures,
tail rotor gearbox failures, or a complete loss of the tail rotor
itself. In any of these cases, the loss of antitorque normally
results in an immediate spinning of the helicopter’s nose.
The helicopter spins to the right in a counterclockwise rotor
system and to the left in a clockwise system. This discussion
is for a helicopter with a counterclockwise rotor system. The
severity of the spin is proportionate to the amount of power
being used and the airspeed. An antitorque failure with a high
power setting at a low airspeed results in a severe spinning
to the right. At low power settings and high airspeeds, the
spin is less severe. High airspeeds tend to streamline the
helicopter and keep it from spinning.
If a tail rotor failure occurs, power must be reduced in order to
reduce main rotor torque. The techniques differ depending on
whether the helicopter is in flight or in a hover, but ultimately
require an autorotation. If a complete tail rotor failure occurs
while hovering, enter a hovering autorotation by rolling off
the throttle. If the failure occurs in forward flight, enter a
normal autorotation by lowering the collective and rolling
off the throttle. If the helicopter has enough forward airspeed
(close to cruising speed) when the failure occurs, and
depending on the helicopter design, the vertical stabilizer
may provide enough directional control to allow the pilot to
maneuver the helicopter to a more desirable landing sight.
Applying slight cyclic control opposite the direction of yaw
compensates for some of the yaw. This helps in directional
control, but also increases drag. Care must be taken not to
lose too much forward airspeed because the streamlining
effect diminishes as airspeed is reduced. Also, more altitude is
required to accelerate to the correct airspeed if an autorotation
is entered at a low airspeed.
11-16
The throttle or power lever on some helicopters is not located
on the collective and readily available. Faced with the loss
of antitorque, the pilot of these models may need to achieve
forward flight and let the vertical fin stop the yawing rotation.
With speed and altitude the pilot will have the time to set
up for an autorotative approach and set the power control
to idle or off as the situation dictates. At low altitudes, the
pilot may not be able to reduce the power setting and enter
the autorotation before impact.
A mechanical control failure limits or prevents control of tail
rotor thrust and is usually caused by a stuck or broken control
rod or cable. While the tail rotor is still producing antitorque
thrust, it cannot be controlled by the pilot. The amount of
antitorque depends on the position at which the controls jam
or fail. Once again, the techniques differ depending on the
amount of tail rotor thrust, but an autorotation is generally
not required.
The specific manufacturer’s procedures should always be
followed. The following is a generalized description of
procedures when more specific procedures are not provided.
Landing—Stuck Left Pedal
A stuck left pedal (high power setting), which might be
experienced during takeoff or climb conditions, results in
the left yaw of the helicopter nose when power is reduced.
Rolling off the throttle and entering an autorotation only
makes matters worse. The landing profile for a stuck left
pedal is best described as a normal to steep approach angle to
arrive approximately 2–3 feet landing gear height above the
intended landing area as translational lift is lost. The steeper
angle allows for a lower power setting during the approach
and ensures that the nose remains to the left.
Upon reaching the intended touchdown area and at the
appropriate landing gear height, increase the collective
smoothly to align the nose with the landing direction and
cushion the landing. A small amount of forward cyclic is
helpful to stop the nose from continuing to the right and
directs the aircraft forward and down to the surface. In certain
wind conditions, the nose of the helicopter may remain to the
left with zero to near zero groundspeed above the intended
touchdown point. If the helicopter is not turning, simply lower
the helicopter to the surface. If the nose of the helicopter is
turning to the right and continues beyond the landing heading,
roll the throttle toward flight idle the amount necessary to
stop the turn while landing. If the helicopter is beginning to
turn left, the pilot should be able to make the landing prior
to the turn rate becoming excessive. However, if the turn rate
begins to increase prior to the landing, simply add power to
make a go-around and return for another landing.
Landing—Stuck Neutral or Right Pedal
The landing profile for a stuck neutral or a stuck right pedal
is a low-power approach terminating with a running or rollon landing. The approach profile can best be described as a
shallow to normal approach angle to arrive approximately
2–3 feet landing gear height above the intended landing
area with a minimum airspeed for directional control. The
minimum airspeed is one that keeps the nose from continuing
to yaw to the right.
Upon reaching the intended touchdown area and at the
appropriate landing gear height, reduce the throttle as
necessary to overcome the yaw effect if the nose of the
helicopter remains to the right of the landing heading. The
amount of throttle reduction will vary based on power applied
and winds. The higher the power setting used to cushion the
landing, the more the throttle reduction will be. A coordinated
throttle reduction and increased collective will result in a very
smooth touchdown with some forward ground speed. If the
nose of the helicopter is to the left of the landing heading,
a slight increase in collective or aft cyclic may be used to
align the nose for touchdown. The decision to land or go
around has to be made prior to any throttle reduction. Using
airspeeds slightly above translational lift may be helpful to
ensure that the nose does not continue yawing to the right. If
a go-around is required, increasing the collective too much or
too rapidly with airspeeds below translational lift may cause
a rapid spinning to the right.
Once the helicopter has landed and is sliding/rolling to a
stop, the heading can be controlled with a combination of
collective, cyclic and throttle. To turn the nose to the right,
raise the collective or apply aft cyclic. The throttle may be
increased as well if it is not in the full open position. To turn
the nose to the left, lower the collective or apply forward
cyclic. The throttle may be decreased as well if it is not
already at flight idle.
Loss of Tail Rotor Effectiveness (LTE)
Loss of tail rotor effectiveness (LTE) or an unanticipated
yaw is defined as an uncommanded, rapid yaw towards the
advancing blade which does not subside of its own accord.
It can result in the loss of the aircraft if left unchecked. It is
very important for pilots to understand that LTE is caused
by an aerodynamic interaction between the main rotor and
tail rotor and not caused from a mechanical failure. Some
helicopter types are more likely to encounter LTE due to the
normal certification thrust produced by having a tail rotor
that, although meeting certification standards, is not always
able to produce the additional thrust demanded by the pilot.
A helicopter is a collection of compromises. Compare the
size of an airplane propeller to that of a tail rotor. Then,
consider the horsepower required to run the propeller. For
example, a Cessna 172P is equipped with a 160-horsepower
(HP) engine. A Robinson R-44 with a comparably sized tail
rotor is rated for a maximum of 245 HP. If you assume the
tail rotor consumes 50 HP, only 195 HP remains to drive
the main rotor. If the pilot were to apply enough collective
to require 215 HP from the engine, and enough left pedal to
require 50 HP for the tail rotor, the resulting engine overload
would lead to one of two outcomes: slow down (reduction
in rpm) or premature failure. In either outcome, antitorque
would be insufficient and total lift might be less than needed
to remain airborne.
Every helicopter design requires some type of antitorque
system to counteract main rotor torque and prevent spinning
once the helicopter lifts off the ground. A helicopter is heavy,
and the powerplant places a high demand on fuel. Weight
penalizes performance, but all helicopters must have an
antitorque system, which adds weight. Therefore, the tail
rotor is certified for normal flight conditions. Environmental
forces can overwhelm any aircraft, rendering the inherently
unstable helicopter especially vulnerable.
As with any aerodynamic condition, it is very important
for pilots to not only understand the definition of terms but
more importantly how and why they happen, how to avoid
the situation and lastly, how to correct the condition once it
is encountered. We must first understand the capabilities of
the aircraft or even better what it is not capable of doing. For
example, if you were flying a helicopter with a maximum
gross weight of 5,200 lbs, would a pilot knowingly try to take
on fuel, baggage and passengers causing the weight to be
5,500 lbs? A wise professional pilot should not ever exceed
the certificated maximum gross weight or performance flight
weight for any aircraft. The manuals are written for safety
and reliability. The limitations and emergency procedures
are stressed because lapses in procedures or exceeding
limitations can result in aircraft damage or human fatalities.
At the very least, exceeding limitations will increase the costs
of maintenance and ownership of any aircraft and especially
helicopters.
Overloaded parts will fail before their designed lifetime.
There are no extra parts in helicopters. The respect and
discipline pilots exercise for following flight manuals should
also be applied to understanding aerodynamic conditions.
If flight envelopes are exceeded, the end results can be
catastrophic.
LTE is an aerodynamic condition and is the result of a control
margin deficiency in the tail rotor. It can affect all single rotor
helicopters that utilize a tail rotor of some design. The design
of main and tail rotor blades and the tail boom assembly can
11-17
The airflow relative to the helicopter;
a. Worst case—relative wind within ±15° of the
10 o’clock position, generating vortices that
can blow directly into the tail rotor. This is
dictated by the characteristics of the helicopters
aerodynamics of tailboom position, tailrotor size
and position relative to the main rotor and vertical
stabilizer, size and shape. [Figure 11-11]
b.
Weathercock stability—tailwinds from 120° to
240° [Figure 11 -12], such as left crosswinds,
causing high pilot workload.
c.
Tail rotor vortex ring state (210° to
330°). [Figure 11-13] Winds within this region
will result in the development of the vortex ring
state of the tail rotor.
33
360°
0°
30
°
20
k
°
60
15 kno
ts
10 kn
ots
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Wind
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R
vort egion
ex
int of d
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31
285
90°
270°
°
0°
24
0°
12
0°
0°
21
LTE is a condition that occurs when the flow of air through a
tail rotor is altered in some way, either by altering the angle
or speed at which the air passes through the rotating blades
of the tail rotor system. An effective tail rotor relies on a
stable and relatively undisturbed airflow in order to provide
a steady and constant antitorque reaction as discussed in
the previous paragraph. The pitch and angle of attack of the
individual blades will determine the thrust output of the tail
rotor. A change to any of these alters the amount of thrust
generated. A pilot’s yaw pedal input affects a thrust reaction
from the tail rotor. Altering the amount of thrust delivered
for the same yaw input creates an imbalance. Taking this
imbalance to the extreme will result in the loss of effective
control in the yawing plane, and LTE will occur.
6.
15
affect the characteristics and susceptibility of LTE but will not
nullify the phenomenon entirely. Translational lift is obtained
by any amount of clean air through the main rotor system.
Chapter 3 discusses translational lift with respect to the main
rotor blade, explaining that the more clean air there is going
through the rotor system, the more efficient it becomes. The
same holds true for the tail rotor. As the tail rotor works in
less turbulent air, it reaches a point of translational thrust. At
this point, the tail rotor becomes aerodynamically efficient
and the improved efficiency produces more antitorque thrust.
The pilot can determine when the tail rotor has reached
translational thrust. As more antitorque thrust is produced,
the nose of the helicopter yaws to the left (opposite direction
of the tail rotor thrust), forcing the pilot to correct with right
pedal application (actually decreasing the left pedal). This,
in turn, decreases the AOA in the tail rotor blades. Pilots
should be aware of the characteristics of the helicopter they
fly and be particularly aware of the amount of tail rotor pedal
typically required for different flight conditions.
180°
This alteration of tail rotor thrust can be affected by numerous
external factors. The main factors contributing to LTE are:
1.
Airflow and downdraft generated by the main rotor
blades interfering with the airflow entering the tail
rotor assembly.
2.
Main blade vortices developed at the main blade tips
entering the tail rotor.
3.
Turbulence and other natural phenomena affecting the
airflow surrounding the tail rotor.
4.
A high power setting, hence large main rotor
pitch angle, induces considerable main rotor blade
downwash and hence more turbulence than when the
helicopter is in a low power condition.
5.
A slow forward airspeed, typically at speeds where
translational lift and translational thrust are in the
process of change and airflow around the tail rotor
will vary in direction and speed.
11-18
Figure 11-11. Main rotor disk vortex interference.
7.
Combinations (a, b, c) of these factors in a particular
situation can easily require more anti-torque than the
helicopter can generate and in a particular environment
LTE can be the result.
Certain flight activities lend themselves to being more at
high risk to LTE than others. For example, power line and
pipeline patrol sectors, low speed aerial filming/photography
as well as in the Police and Helicopter Emergency Medical
Services (EMS) environments can find themselves in low
and slow situations over geographical areas where the exact
wind speed and direction are hard to determine.
360°
0°
0°
15 kn
o
33
17
4.
Low speed downwind turns.
5.
Large changes of power at low airspeeds.
6.
Low speed flight in the proximity of physical
obstructions that may alter a smooth airflow to both
the main rotor and tail rotor.
°
60
5k
12
°
40
90°
nots
270°
Tailwinds that may alter the onset of translational
lift and translational thrust hence induce high power
demands and demand more anti-torque (left pedal)
than the tail rotor can produce.
ts
30
0°
k
no
10 k n
ots
2
0°
0°
21
ibl
e y
aw
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we
introd
uction by
ath
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c
k
oc
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a
Wind
ss
0°
po
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o
of
bi
gi
lit
y
Pilots who put themselves in situations where the combinations
above occur should know that they are likely to encounter
LTE. The key is to not put the helicopter in a compromising
condition but if it does happen being educated enough to
recognize the onset of LTE and be prepared to quickly react
to it before the helicopter cannot be controlled.
Early detection of LTE followed by the immediate flight
control application of corrective action; applying forward
cyclic to regain airspeed, applying right pedal not left as
necessary to maintain rotor RPM and reducing the collective
thus reducing the high power demand on the tail rotor is the
key to a safe recovery. Pilots should always set themselves
up when conducting any maneuver to have enough height
and space available to recover in the event they encounter
an aerodynamic situation such as LTE.
st
a
360°
0°
0°
15 kn
ots
33
30
°
17
k
°
60
ts
no
10 kn
ots
n
0°
12
e
hn
ug
r o 0°
24
of
90°
nots
5k
ue to tail rot
or
ss d
vo
270°
rte
x
30
ri
0°
n
g
te
15
0°
0°
21
180°
Re
gi
o
Figure 11-13. Tail rotor vortex ring state.
Unfortunately, the aerodynamic conditions that a helicopter
is susceptible to are not explainable in black and white terms.
LTE is no exception. There are a number of contributing
factors but what is more important to understanding LTE
are taking the contributing factors and couple them with
situations that should be avoided. Whenever possible, pilots
should learn to avoid the following combinations:
1.
3.
°
Figure 11-12. Weathercock stability.
Wind
Winds from ±15º of the 10 o’clock position
and probably on around to 5 o’clock position
[Figure 11-11]
30
ts
Re
n
2.
Low and slow flight outside of ground effect.
Understanding the aerodynamic phenomenon of LTE is by far
the most important factor, and the ability and option to either
go around if making an approach or pull out of a maneuver
safely and re-plan, is always the safe option. Having the
ability to fly away from a situation and re-think the possible
options should always be part of a pilot's planning process in
all phases of flight. Unfortunately, there have been many pilots
who have idled a good engine and fully functioning tail rotor
system and autorotated a perfectly airworthy helicopter to the
crash site because they misunderstood or misperceived both
the limitations of the helicopter and the aerodynamic situation.
Main Rotor Disk Interference (285–315°)
Refer to Figure 11-11. Winds at velocities of 10–30 knots
from the left front cause the main rotor vortex to be blown
into the tail rotor by the relative wind. This main rotor
disk vortex causes the tail rotor to operate in an extremely
turbulent environment. During a right turn, the tail rotor
experiences a reduction of thrust as it comes into the area of
the main rotor disk vortex. The reduction in tail rotor thrust
comes from the airflow changes experienced at the tail rotor
as the main rotor disk vortex moves across the tail rotor disk.
11-19
The effect of the main rotor disk vortex initially increases the
AOA of the tail rotor blades, thus increasing tail rotor thrust.
The increase in the AOA requires that right pedal pressure
be added to reduce tail rotor thrust in order to maintain the
same rate of turn. As the main rotor vortex passes the tail
rotor, the tail rotor AOA is reduced. The reduction in the
AOA causes a reduction in thrust and right yaw acceleration
begins. This acceleration can be surprising, since previously
adding right pedal to maintain the right turn rate. This thrust
reduction occurs suddenly, and if uncorrected, develops
into an uncontrollable rapid rotation about the mast. When
operating within this region, be aware that the reduction in
tail rotor thrust can happen quite suddenly, and be prepared
to react quickly to counter this reduction with additional left
pedal input.
Weathercock Stability (120–240°)
In this region, the helicopter attempts to weathervane,
or weathercock, its nose into the relative wind.
[Figure 11-12] Unless a resisting pedal input is made, the
helicopter starts a slow, uncommanded turn either to the right
or left, depending upon the wind direction. If the pilot allows
a right yaw rate to develop and the tail of the helicopter moves
into this region, the yaw rate can accelerate rapidly. In order
to avoid the onset of LTE in this downwind condition, it is
imperative to maintain positive control of the yaw rate and
devote full attention to flying the helicopter.
Tail Rotor Vortex Ring State (210–330°)
Winds within this region cause a tail rotor vortex ring state to
develop. [Figure 11-13] The result is a nonuniform, unsteady
flow into the tail rotor. The vortex ring state causes tail
rotor thrust variations, which result in yaw deviations. The
net effect of the unsteady flow is an oscillation of tail rotor
thrust. Rapid and continuous pedal movements are necessary
to compensate for the rapid changes in tail rotor thrust when
hovering in a left crosswind. Maintaining a precise heading
in this region is difficult, but this characteristic presents
no significant problem unless corrective action is delayed.
However, high pedal workload, lack of concentration, and
overcontrolling can lead to LTE.
When the tail rotor thrust being generated is less than the
thrust required, the helicopter yaws to the right. When
hovering in left crosswinds, concentrate on smooth pedal
coordination and do not allow an uncommanded right yaw to
develop. If a right yaw rate is allowed to build, the helicopter
can rotate into the wind azimuth region where weathercock
stability then accelerates the right turn rate. Pilot workload
during a tail rotor vortex ring state is high. Do not allow a
right yaw rate to increase.
11-20
LTE at Altitude
At higher altitudes where the air is thinner, tail rotor thrust
and efficiency are reduced. Because of the high density
altitude, powerplants may be much slower to respond to
power changes. When operating at high altitudes and high
gross weights, especially while hovering, the tail rotor thrust
may not be sufficient to maintain directional control, and
LTE can occur. In this case, the hovering ceiling is limited
by tail rotor thrust and not necessarily power available. In
these conditions, gross weights need to be reduced and/
or operations need to be limited to lower density altitudes.
This may not be noted as criteria on the performance charts.
Reducing the Onset of LTE
To help reduce the onset of LTE, follow these steps:
1.
Maintain maximum power-on rotor rpm. If the main
rotor rpm is allowed to decrease, the antitorque thrust
available is decreased proportionally.
2.
Avoid tailwinds below airspeeds of 30 knots. If loss
of translational lift occurs, it results in an increased
power demand and additional antitorque pressures.
3.
Avoid OGE operations and high power demand
situations below airspeeds of 30 knots at low altitudes.
4.
Be especially aware of wind direction and velocity
when hovering in winds of about 8–12 knots. A loss
of translational lift results in an unexpected high power
demand and an increased antitorque requirement.
5.
Be aware that if a considerable amount of left pedal
is being maintained, a sufficient amount of left pedal
may not be available to counteract an unanticipated
right yaw.
6.
Be alert to changing wind conditions, which may be
experienced when flying along ridge lines and around
buildings.
7.
Execute slow turns to the right which would limit
the effects of rotating inertia, and the loading on the
tailrotor to control yawing would be decreased.
Recovery Technique
If a sudden unanticipated right yaw occurs, the following
recovery technique should be performed. Apply forward
cyclic control to increase speed. If altitude permits, reduce
power. As recovery is affected, adjust controls for normal
forward flight. A recovery path must always be planned,
especially when terminating to an OGE hover and executed
immediately if an uncommanded yaw is evident.
Collective pitch reduction aids in arresting the yaw rate but
may cause an excessive rate of descent. Any large, rapid
increase in collective to prevent ground or obstacle contact
may further increase the yaw rate and decrease rotor rpm.
The decision to reduce collective must be based on the pilot’s
assessment of the altitude available for recovery.
If the rotation cannot be stopped and ground contact is
imminent, an autorotation may be the best course of action.
Maintain full left pedal until the rotation stops, then adjust
to maintain heading. For more information on LTE, see
Advisory Circular (AC) 90-95, Unanticipated Right Yaw
in Helicopters.
Main Drive Shaft or Clutch Failure
The main drive shaft, located between the engine and the
main rotor gearbox, transmits engine power to the main
rotor gearbox. In some helicopters, particularly those with
piston engines, a drive belt is used instead of a drive shaft.
A failure of the drive shaft clutch or belt has the same effect
as an engine failure because power is no longer provided to
the main rotor and an autorotation must be initiated. There
are a few differences, however, that need to be taken into
consideration. If the drive shaft or belt breaks, the lack of any
load on the engine results in an overspeed. In this case, the
throttle must be closed in order to prevent any further damage.
In some helicopters, the tail rotor drive system continues to
be powered by the engine even if the main drive shaft breaks.
In this case, when the engine unloads, a tail rotor overspeed
can result. If this happens, close the throttle immediately and
enter an autorotation. The pilot must be knowledgeable of
the specific helicopter’s system and failure modes.
Pilots should keep in mind that when there is any suspected
mechanical malfunction, first and foremost they should
always attempt to maintain rotor RPM. If the rotor RPM
is at the normal indication with normal power settings, an
instrument failure might be occurring and it would be best
to fly the helicopter to a safe landing area. If the rotor RPM
is in fact decreasing or low, then there is a drive line failure.
Hydraulic Failure
Many helicopters incorporate the use of hydraulic actuators
to overcome high control forces. A hydraulic system consists
of actuators, also called servos, on each flight control; a
pump, which is usually driven by the main rotor gearbox;
and a reservoir to store the hydraulic fluid. A switch in the
cockpit can turn the system off, although it is left on during
normal conditions. A pressure indicator in the cockpit may
be installed to monitor the system.
An impending hydraulic failure can be recognized by a
grinding or howling noise from the pump or actuators,
increased control forces and feedback, and limited control
movement. The required corrective action is stated in detail
in the appropriate RFM. However, in most cases, airspeed
needs to be reduced in order to reduce control forces. The
hydraulic switch and circuit breaker should be checked and
recycled. If hydraulic power is not restored, make a shallow
approach to a running or roll-on landing. This technique is
used because it requires less control force and pilot workload.
Additionally, the hydraulic system should be disabled by
placing the switch in the off position. The reason for this is to
prevent an inadvertent restoration of hydraulic power, which
may lead to overcontrolling near the ground.
In those helicopters in which the control forces are so high
that they cannot be moved without hydraulic assistance, two
or more independent hydraulic systems are installed. Some
helicopters use hydraulic accumulators to store pressure that
can be used for a short time while in an emergency if the
hydraulic pump fails. This gives enough time to land the
helicopter with normal control.
Governor or Fuel Control Failure
Governors and fuel control units automatically adjust engine
power to maintain rotor rpm when the collective pitch is
changed. If the governor or fuel control unit fails, any change
in collective pitch requires manual adjustment of the throttle
to maintain correct rpm. In the event of a high side failure,
the engine and rotor rpm tend to increase above the normal
range. If the rpm cannot be reduced and controlled with the
throttle, close the throttle and enter an autorotation. If the
failure is on the low side, normal rpm may not be attainable,
even if the throttle is manually controlled. In this case, the
collective has to be lowered to maintain rotor rpm. A running
or roll-on landing may be performed if the engine can
maintain sufficient rotor rpm. If there is insufficient power,
enter an autorotation. As stated previously in this chapter,
before responding to any type of mechanical failure, pilots
should confirm that rotor rpm is not responding to flight
control inputs. If the rotor rpm can be maintained in the
green operating range, the failure is in the instrument, and
not mechanical.
Abnormal Vibration
With the many rotating parts found in helicopters, some
vibration is inherent. A pilot needs to understand the
cause and effect of helicopter vibrations because abnormal
vibrations cause premature component wear and may even
result in structural failure. With experience, a pilot learns
what vibrations are normal and those that are abnormal,
and can then decide whether continued flight is safe or not.
Helicopter vibrations are categorized into low, medium, or
high frequency.
11-21
Low-Frequency Vibrations
Low-frequency vibrations (100–500 cycles per minute)
usually originate from the main rotor system. The main rotor
operational range, depending on the helicopter, is usually
between 320 and 500 rpm. A rotor blade that is out of track
or balance will cause a cycle to occur with every rotation.
The vibration may be felt through the controls, the airframe,
or a combination of both. The vibration may also have a
definite direction of push or thrust. It may be vertical, lateral,
horizontal, or even a combination of these. Normally, the
direction of the vibration can be determined by concentrating
on the feel of the vibration, which may push a pilot up and
down, backwards and forwards, or in the case of a blade
being out of phase, from side to side. The direction of the
vibration and whether it is felt in the controls or the airframe
is important information for the mechanic when he or she
troubleshoots the source. Out-of-track or out-of-balance
main rotor blades, damaged blades, worn bearings, dampers
out of adjustment, or worn parts are possible causes of low
frequency vibrations.
rpm internally, but common gearbox speeds are in the 1,000
to 3,000 rpm range for the output shaft. The vibrations in
turbine engines may be short lived as the engine disintegrates
rapidly when damaged due to high rpm and the forces present.
Tracking and Balance
Modern equipment used for tracking and balancing the main
and tail rotor blades can also be used to detect other vibrations
in the helicopter. These systems use accelerometers mounted
around the helicopter to detect the direction, frequency, and
intensity of the vibration. The built-in software can then
analyze the information, pinpoint the origin of the vibration,
and suggest the corrective action.
The use of a system such as a health and usage monitoring
system (HUMS) provides the operator the ability to record
engine and gearbox performance and provide rotor track and
balance. This system has been around for over 30 years and
is now becoming more affordable, more capable, and more
commonplace in the rotorcraft industry.
Medium- and High-Frequency Vibrations
Multiengine Emergency Operations
Medium-frequency vibrations (1,000–2,000 cycles per
minute) range between the low frequencies of the main rotor
(100–500 cycles per minute) and the high frequencies (2,100
cycles per minute or higher) of the engine and tail rotor.
Depending on the helicopter, medium-frequency vibration
sources may be engine and transmission cooling fans, and
accessories such as air conditioner compressors, or driveline
components. Medium-frequency vibrations are felt through
the entire airframe, and prolonged exposure to the vibrations
will result in greater pilot fatigue.
Single-Engine Failure
When one engine has failed, the helicopter can often maintain
altitude and airspeed until a suitable landing site can be
selected. Whether or not this is possible becomes a function
of such combined variables as aircraft weight, density
altitude, height above ground, airspeed, phase of flight,
single-engine capability, and environmental response time
and control technique may be additional factors. Caution
must be exercised to correctly identify the malfunctioning
engine since there is no telltale yawing as occurs in most
multiengine airplanes. Shutting down the wrong engine
could be disastrous!
Most tail rotor vibrations fall into the high-frequency range
(2,100 cycles per minute or higher) and can be felt through
the tail rotor pedals as long as there are no hydraulic actuators
to dampen out the vibration. This vibration is felt by the pilot
through his or her feet, which are usually “put to sleep” by
the vibration. The tail rotor operates at approximately a 6:1
ratio with the main rotor, meaning for every one rotation of
the main rotor the tail rotor rotates 6 times. A main rotor
operating rpm of 350 means the tail rotor rpm would be 2,100
rpm. Any imbalance in the tail rotor system is very harmful as
it can cause cracks to develop and rivets to work loose. Piston
engines usually produce a normal amount of high-frequency
vibration, which is aggravated by engine malfunctions, such
as spark plug fouling, incorrect magneto timing, carburetor
icing and/or incorrect fuel/air mixture. Vibrations in turbine
engines are often difficult to detect as these engines operate
at a very high rpm. Turbine engine vibration can be at 30,000
11-22
Even when flying multiengine powered helicopters, rotor rpm
must be maintained at all costs, because fuel contamination
has been documented as the cause for both engines failing
in flight.
Dual-Engine Failure
The flight characteristics and the required crew member
control responses after a dual-engine failure are similar to
those during a normal power-on descent. Full control of the
helicopter can be maintained during autorotational descent.
In autorotation, as airspeed increases above 70–80 knots
indicated airspeed (KIAS), the rate of descent and glide
distance increase significantly. As airspeed decreases below
approximately 60 KIAS, the rate of descent increases and
glide distance decreases.
Lost Procedures
Pilots become lost while flying for a variety of reasons, such
as disorientation, flying over unfamiliar territory, or visibility
that is low enough to render familiar terrain unfamiliar. When
a pilot becomes lost, the first order of business is to fly the
aircraft; the second is to implement lost procedures. Keep
in mind that the pilot workload will be high and increased
concentration is necessary. If lost, always remember to
look for the practically invisible hazards such as wires by
searching for their support structures, such as poles or towers,
which are almost always near roads.
If lost, follow common sense procedures.
•
Try to locate any large landmarks, such as lakes, rivers,
towers, railroad tracks, or Interstate highways. If a
landmark is recognized, use it to find the helicopter’s
location on the sectional chart. If flying near a town or
city, a pilot may be able to read the name of the town
on a water tower or even land to ask for directions.
•
If no town or city is nearby, the first thing a pilot
should do is climb. An increase in altitude increases
radio and navigation reception range as well as radar
coverage.
•
Navigation aids, dead reckoning, and pilotage are
skills that can be used as well.
•
Do not forget air traffic control—controllers assist
pilots in many ways, including finding a lost
helicopter. Once communication with ATC has been
established, follow their instructions.
These common sense procedures can be easily remembered by
using the four Cs: Climb, Communicate, Confess, and Comply.
•
•
Climb for a better view, improved communication and
navigation reception, and terrain avoidance.
Communicate by calling the nearest flight service
station (FSS )/automated flight service station (AFSS)
on 122.2 MHz. If the FSS/AFSS does not respond,
call the nearest control tower, center, or approach
control. For frequencies, check the chart in the vicinity
of the last known position. If that fails, switch to
the emergency radio frequency (121.5 MHz) and
transponder code (7700).
•
Report the lost situation to air traffic control and
request help.
•
Comply with controller instructions.
Pilots should understand the services provided by ATC and
the resources and options available. These services enable
pilots to focus on aircraft control and help them make better
decisions in a time of stress.
When contacting ATC, pilots should provide as much
information as possible because ATC uses the information
to determine what kind of assistance it can provide with
available assets and capabilities. Information requirements
vary depending on the existing situation, but at a minimum
a pilot should provide the following information:
•
Aircraft identification and type
•
Nature of the emergency
•
Aviator’s desires
To reduce the chances of getting lost in the first place, use
flight following when it is available, monitor checkpoints no
more than 25 miles apart, keep navigation aids such as VORs
tuned in, and maintain good situational awareness.
Getting lost is a potentially dangerous situation for any
aircraft, especially when low on fuel. Due to the helicopter’s
unique ability to land almost anywhere, pilots have more
flexibility than other aircraft as to landing site. An inherent
risk associated with being lost is waiting too long to land in a
safe area. Helicopter pilots should land before fuel exhaustion
occurs because maneuvering with low fuel levels could cause
the engine to stop due to fuel starvation as fuel sloshes or
flows away from the pickup port in the tank.
If lost and low on fuel, ALWAYS land with fuel on board
to enable a safe landing. Preferably, land near a road or
in an area allowing plenty of room for another helicopter
to land in the same area safely. Having fuel delivered is a
minor inconvenience when compared to a crash. Fuel on
board after landing allows use of the radios as well as heat
in colder climates.
Emergency Equipment and Survival Gear
Both Canada and Alaska require pilots to carry survival
gear. Always carry survival gear when flying over rugged
and desolate terrain. The items suggested in Figure 11-14
are both weather and terrain dependent. The pilot also needs
to consider how much storage space the helicopter has and
how the equipment being carried affects the overall weight
and balance of the helicopter.
Chapter Summary
Emergencies should always be anticipated. Knowledge
of the helicopter, possible malfunctions and failures, and
methods of recovery can help the pilot avoid accidents and
be a safer pilot. Helicopter pilots should always expect the
worse hazards and possible aerodynamic effects and plan for
a safe exit path or procedure to compensate for the hazard.
11-23
EMERGENCY EQUIPMENT AND SURVIVAL GEAR
Food cannot be subject to deterioration due to heat or cold. There
should be at least 10,000 calories for each person on board, and it
should be stored in a sealed waterproof container. It should have
been inspected by the pilot or his representative within the previous
6 months, and bear a label verifying the amount and satisfactory
condition of the contents.
A supply of water
Cooking utensils
Matches in a waterproof container
A portable compass
An ax weighing at least 2.5 pounds with a handle not less than 28 inches
in length
A flexible saw blade or equivalent cutting tool
30 feet of snare wire and instructions for use
Fishing equipment, including still-fishing bait and gill net with not more
than a two-inch mesh
Mosquito nets or netting and insect repellent sufficient to meet the
needs of all persons aboard, when operating in areas where insects
are likely to be hazardous
A signaling mirror
At least three pyrotechnic distress signals
A sharp, quality jackknife or hunting knife
A suitable survival instruction manual
Flashlight with spare bulbs and batteries
Portable emergency locator transmitter (ELT) with spare batteries
Stove with fuel or a self-contained means of providing heat for cooking
Tent(s) to accommodate everyone on board
Additional items for winter operations:
• Winter sleeping bags for all persons when the
temperature is expected to be below 7 °C
• Two pairs of snow shoes
• Spare ax handle
• Ice chisel
• Snow knife or saw knife
Figure 11-14. Emergency equipment and survival gear.
11-24
Chapter 12
Attitude Instrument Flying
Introduction
Attitude instrument flying is the control of a helicopter by
reference to the instruments rather than by outside visual
cues. The pilot substitutes the various reference points
on the helicopter and the natural horizon with the flight
instruments. Control changes, required to produce a given
attitude by reference to instruments, are identical to those
used in helicopter visual flight rules (VFR) flight. This chapter
introduces basic instrument training. It is a building block
toward attaining an instrument rating, but is not a substitute
for the more detailed information found in the Instrument
Flying Handbook (FAA-H-8083-15) and the Advanced
Avionics Handbook (FAA-H-8083-6).
12-1
This chapter is designed to enable a pilot to maintain
control of the helicopter during a 180° turn in the case of
an inadvertent encounter with instrument meteorological
conditions (IMC). if equipped for IMC conditions. If not,
the pilot should strictly maintain visual meteorological
conditions (VMC) rather than penetrating clouds or fog and
land as necessary.
that the airspeed indication might be unreliable below a
certain airspeed due to rotor downwash.
Flight Instruments
Turn Indicator
The needle portion of the turn-and-slip indicator shows
direction of turn and rate. [Figure 12-1] For instance, if
the needle is centered on the standard rate turn marking,
the helicopter will complete a 360˚ turn in 2 minutes.
[Figure 12-2] Another part of the turn-and-slip indicator is
the inclinometer. The position of the ball defines whether
the turn is coordinated or not. The helicopter is not in a
coordinated turn any time the ball is not centered, and usually
requires an input to the antitorque pedals and angle of bank
to correct it.
Operational flight instruments free the pilot from the necessity
of maintaining visual contact with the ground. When attitude
instrument flying, it is crucial for the pilot to understand how
a particular instrument or system functions, including its
indications and limitations. It is also important for the pilot
to ensure the helicopter’s instruments are operating properly
prior to a flight.
A helicopter pilot can easily make a preliminary check of
flight instruments at a hover prior to departing on a flight. For
example, as collective is increased, the altimeter indicates a
decrease in altitude by about 20 feet for most helicopters. This
decrease is due to the increase in air pressure between the
main rotor and the ground (ground effect). As the helicopter
rises to a hover, the altimeter usually recovers to indicate
field elevation.
Altimeter
Before lift-off, set the altimeter to the current setting. If the
altimeter indicates within 75 feet of the actual elevation, the
altimeter is generally considered acceptable for instrument use.
Horizontal gyro
Gyro rotation
During the hover, heading indicators can be checked for
freedom of movement and correct indications and the
freedom of the slip indicator can be verified. The proper
operation of the attitude indicator can be checked during the
hover by gently pitching the nose of the helicopter up and
down and rolling from side to side.
Instrument Check
The pitot-static system and associated instruments—airspeed
indicator, altimeter, and vertical speed indicator—are usually
very reliable. Errors are generally caused when the pitot or
static openings are blocked. This may be caused by dirt, ice
formation, or insects. Check the pitot and static openings
for obstructions during the preflight. Turn indicators and
magnetic compass are also important components of attitude
instrument flying. Instrument checks ensure reliability of
these instruments.
Airspeed Indicator
During the preflight, ensure that the pitot tube, drain hole,
and static ports are unobstructed. Before lift-off, make sure
the airspeed indicator is reading zero. If there is a strong
wind blowing directly at the helicopter, the airspeed indicator
may read higher than zero, depending on the wind speed and
direction. As takeoff begins, make sure the airspeed indicator
is increasing at an appropriate rate. Keep in mind, however,
12-2
Gimbal rotation
Figure 12-1. Turn-and-slip indicator.
1
2
L
R
2 MIN TURN
DC
ELEC
3
L
R
2 MIN TURN
DC
ELEC
L
R
2 MIN TURN
DC
ELEC
Inclinometer
Figure 12-2. In a coordinated turn (instrument 1), the ball is
centered. In a skid (instrument 2), the rate of turn is too great for
the angle of bank, and the ball moves to the outside of the turn. The
pilot must decrease right pedal and add left pedal to center the ball.
Conversely, in a slip (instrument 3), the rate of turn is too small for
the angle of bank, and the ball moves to the inside of the turn. The
pilot must add left pedal to center the ball.
During preflight, check to see that the inclinometer is full of
fluid and has no air bubbles. The ball should also be resting
at its lowest point. Since almost all gyroscopic instruments
installed in a helicopter are electrically driven, check to see
that the power indicators are displaying off indications. Turn
the master switch on and listen to the gyros spool up. There
should be no abnormal sounds, such as a grinding sound, and
the power-out indicator flags should not be displayed. After
engine start and before lift-off, set the direction indicator
to the magnetic compass. During hover turns, check the
heading indicator for proper operation and ensure that it has
not precessed significantly. The turn indicator should also
indicate a turn in the correct direction.
Magnetic Compass
The magnetic compass is one of the basic instruments
required by Title 14 of the Code of Federal Regulations (14
CFR) part 91 for both VFR and instrument flight rules (IFR)
flight. The compass can be one of two types: wet (the compass
is suspended in fluid) or vertical.
Prior to flight, ensure a wet compass is full of fluid. During
hover turns, the compass should swing freely and indicate
known headings. Because a magnetic directional indicator is
required for all flights, any malfunctions must be corrected
prior to flight.
Helicopter Control and Performance
Helicopter control is accomplished by controlling the
aircraft’s attitude and power output. Attitude is the
relationship of its longitudinal and lateral axes to the earth’s
horizon. When flying in instrument flight conditions, the pilot
controls the attitude of the helicopter by referencing the flight
instruments and manipulating the power output of the engine
to achieve the desired performance. This method can be used
to achieve a specific performance level enabling a pilot to
perform any basic instrument maneuver. The instrumentation
can be broken up into three different categories: control,
performance, and navigation.
See FAA-H-8083-15, Instrument Flying Handbook for a
detailed discussion of these three categories. Although this
chapter discusses helicopter instrument flying, the concepts
in general are similar to airplane attitude instrument flying.
Helicopter Control
Control of the helicopter is the result of accurately
interpreting the flight instruments and translating these
readings into correct control responses. Helicopter control
involves adjustment to pitch, bank, power, and trim in order
to achieve a desired flightpath.
Pitch attitude control is control of the movement of
the helicopter about its lateral axis. After interpreting
the helicopter’s pitch attitude by reference to the pitch
instruments (attitude indicator, altimeter, airspeed indicator,
and VSI), cyclic control adjustments are made to affect the
desired pitch attitude. A pilot transitioning from airplanes
to helicopters must understand that the attitude indicator is
mounted in the airframe beneath the main rotor system and
does not directly indicate what the main rotor system is doing
to the flightpath. Therefore, the helicopter can take off and
climb with the nose below the horizon. The helicopter can
slow down and land with the nose above the horizon.
In contrast, the airplane must be pointed generally in the
direction of travel (up or down) since the attitude indicator
is firmly attached to the airframe that is firmly attached to
the wings. The helicopter tends to fly through the air at some
stabilized attitude, an effect developed by the horizontal
stabilizer and designed to minimize drag in forward flight.
As a helicopter begins to take off, acceleration begins. As the
airflow increases over the horizontal stabilizer, it produces a
downward force to bring the nose into a stabilized attitude
to streamline the airframe into the relative wind. Therefore,
the helicopter’s attitude indicator is about level when at a
stable airspeed and altitude. A nose-low attitude indicates
acceleration, not necessarily a descent, and a nose-high attitude
indicates a decelerating attitude, not necessarily a climb.
These effects make the helicopter pilot interpretation of
the instruments even more important because the pilot
must integrate the results of the entire instrument scan to
achieve complete situational awareness of the helicopter’s
to flightpath.
Bank attitude control is controlling the angle made by
the lateral tilt of the rotor and the natural horizon, or the
movement of the helicopter about its longitudinal axis (side
to side). After interpreting the helicopter’s bank instruments
(attitude indicator, heading indicator, and turn indicator),
cyclic control adjustments are made to attain the desired
bank attitude.
Power control is the application of collective pitch with
corresponding throttle control, where applicable. In straightand-level flight, changes in collective pitch are made to
correct for altitude deviations if the error is more than 100
feet, or the airspeed is off by more than 10 knots. If the error
is less than that amount, use a slight cyclic climb or descent.
When flying a helicopter by reference to the instruments,
pilots should know the approximate power settings required
for a particular helicopter in various load configurations and
flight conditions.
12-3
Force or cyclic trim, in helicopters, refers to the use of the
cyclic centering button, if the helicopter is so equipped, to
relieve cyclic pressures. Trim also refers to the use of pedal
adjustment to center the ball of the turn indicator. Pedal trim
is required during all power changes.
The proper adjustment of collective pitch and cyclic friction
helps pilots relax during instrument flight. Friction may be
adjusted to minimize overcontrolling and to prevent creeping,
but not applied to such a degree that control movement
is limited. In addition, many helicopters equipped for
instrument flight contain stability augmentation systems or
an autopilot to help relieve pilot workload.
See FAA-H-8083-15, Instrument Flying Handbook, for a
detailed explanation and illustrations concerning helicopter
attitude instrument flying.
Common Errors of Attitude Instrument
Flying
Fixation
Fixation, or staring at one instrument, is a common error
observed in pilots first learning to utilize instruments.
The pilot may initially fixate on an instrument and make
adjustments with reference to that instrument alone.
Omission
Another common error associated with attitude instrument
flying is omission of an instrument from the cross-check.
Pilots tend to omit the stand-by instruments, as well as the
magnetic compass from their scans. The position of the
instrument is often the reason for the omission. One of the
most commonly omitted instruments from the scan is the
slip/skid indicator.
Emphasis
In initial training, placing emphasis on a single instrument
is very common and can become a habit if not corrected.
When the importance of a single instrument is elevated above
another, the pilot begins to rely solely on that instrument
for guidance. When rolling out of a 180° turn, the attitude
indicator, heading indicator, slip/skid indicator, and altimeter
need to be referenced. If a pilot omits the slip/skid indicator,
coordination is sacrificed.
Inadvertent Entry into IMC
Prior to any flight, day or night, an inadvertent IMC plan
should be carefully planned and, if possible, rehearsed.
Many aircraft mishaps can be blamed on the pilot’s inability
to recover an aircraft after inadvertently entering IMC. The
desire to stay outside visually is very strong and can only
be overcome through training. IMC-trained helicopter pilots
should climb to a safe altitude free of obstacles and obtain an
12-4
instrument clearance from ATC. However, for the nonrated
pilot and, more importantly, a non-IFR equipped helicopter,
remaining VMC is critical. Pilots who are not trained in IMC
have a tendency to try and chase favorable weather by flying
just above the tree tops or following roads. The thought
process is that as long as they can see what is below them,
then they can fly to their intended destination. Experience
shows us that continuing VFR flight in IMC is often fatal.
Pilots get too fixated on what they see below them and fail
to see what is ahead of them, such as power lines, towers,
and taller trees. By the time the pilot sees the obstacle, it is
too close to avoid collision. Helicopter pilots should always
remain aware of flight visibility by comparing how much can
be seen ahead. As soon as the pilot notices a marked decrease
in visibility, that pilot must reevaluate the flight plan and
landing options. A suitable landing area can always be used
to sit out bad weather and let conditions improve.
When planning for a night flight, pilots should carefully
plan the flight over navigable routes with sufficient check
points to ensure clearance from obstructions. Descents
should be planned over known and easily identifiable areas.
Deteriorating weather is even harder to detect at night;
therefore, pilots should constantly evaluate the weather
throughout the flight. Below are some basic steps to help the
pilot remain in VMC throughout the flight.
1.
Come to a hover if able or begin very slow flight just
above translational lift speeds and land at the nearest
safe area.
2.
Slowly turn around and proceed back to VMC weather
or first safe landing area if the weather ahead becomes
questionable.
3.
Do not proceed further on a course when the terrain
ahead is not clearly discernable.
4.
Always have a safe landing area in mind for every
flight and always be aware of the safe landing area’s
location.
5.
Study the route whenever possible before flying it and
ensure to stay on course throughout the flight.
There are five basic steps that every pilot should be ultimately
familiar with and should be executed immediately after
inadvertently entering IMC.
1.
Attitude—level the wings on the attitude indicator,
both pitch and bank.
2.
Heading—pick a heading that is known to be free of
obstacles and maintain it. This may be 180° from your
current heading.
3.
Power—adjust to a climb power setting.
4.
Airspeed—adjust to a climb airspeed.
5.
Trim—maintain coordinated flight so that an unusual
attitude will not develop.
Glass Cockpit or Advanced Avionics
Aircraft
A glass cockpit is an aircraft cockpit with an electronic flight
display (EFD). [Figure 12-3] While a traditional cockpit
relies on numerous mechanical gauges to display information,
a glass cockpit utilizes several computer displays that can
be adjusted to display flight information as needed. This
simplifies aircraft operation and navigation and allows a
pilot to focus only on the most pertinent information. Refer
to FAA-H-8083-6, Advanced Avionics Handbook, for more
detailed information and illustrations.
Figure 12-3. Example of a glass cockpit.
Chapter Summary
This chapter introduced the pilot to attitude instrument
flight and flight decisions in a helicopter. A more detailed
exploration of the topics discussed in this chapter can be
found in FAA-H-8083-15, Instrument Flying Handbook;
FAA-H-8083-6, Advanced Avionics Handbook; and
FAA-H-8083-25, Pilot’s Handbook of Aeronautical
Knowledge.
12-5
12-6
Chapter 13
Night Operations
Introduction
Pilots rely more on vision than on any other sense to orient
themselves in flight. The following visual factors contribute
to flying performance: good depth perception for safe
landings, good visual acuity to identify terrain features and
obstacles in the flightpath, and good color vision. Although
vision is the most accurate and reliable sense, visual cues can
be misleading, contributing to incidents occurring within the
flight environment. Pilots must be aware of and know how
to compensate effectively for the following:
•
Physical deficiency or self-imposed stress, such as
smoking, which limits night-vision capability
•
Visual cue deficiencies
•
Limitations in visual acuity, dark adaptation, and color
and depth perception
For example, at night, the unaided eye has degraded
visual acuity. For more information on night operations
reference Chapter 16, pages 16-20 of the Pilots Handbook
of Aeronautical Knowledge.
13-1
Visual Deficiencies
Night Myopia
At night, blue wavelengths of light prevail in the visible
portion of the spectrum. Therefore, slightly nearsighted
(myopic) individuals viewing blue-green light at night may
experience blurred vision. Even pilots with perfect vision find
that image sharpness decreases as pupil diameter increases.
For individuals with mild refractive errors, these factors
combine to make vision unacceptably blurred unless they
wear corrective glasses. Another factor to consider is “dark
focus.” When light levels decrease, the focusing mechanism
of the eye may move toward a resting position and make the
eye more myopic. These factors become important when
pilots rely on terrain features during unaided night flights.
Practicing good light discipline is very important and helps
pilots to retain their night adaptation. Keeping the cockpit
lighting on dim allows the pilot to better identify outside
details, unmarked hazards such as towers less than 200'
AGL, and unimproved landing sites with no hazard lighting.
A simple exercise that shows the difference in light contrast
would be to go out to a very dark road and turn the dash
board lights down very low or off and let your eyes adjust
to the ambient light level. Then, turn the dash board lights
up and note how the outside features disappear. The same
concept applies to cockpit lighting and being able to see the
surrounding terrain and obstacles. [Figure 13-1] Special
corrective lenses can be prescribed to pilots who experience
night myopia .
Hyperopia
Hyperopia is also caused by an error in refraction. In a
hyperopic state, when a pilot views a near image, the actual
focal point of the eye is behind the retinal plane (wall),
causing blurred vision. Objects that are nearby are not seen
clearly; only more distant objects are in focus. This problem,
is referred to as farsightedness.
Astigmatism
An unequal curvature of the cornea or lens of the eye causes
this condition. A ray of light is spread over a diffused area
in one meridian. In normal vision, a ray of light is sharply
focused on the retina. Astigmatism is the inability to
focus different meridians simultaneously. If, for example,
astigmatic individuals focus on power poles (vertical),
the wires (horizontal) are out of focus for most of them.
[Figure 13-2]
Presbyopia
This condition is part of the normal aging process, which
causes the lens to harden. Beginning in the early teens, the
human eye gradually loses the ability to accommodate for
and focus on nearby objects. When people are about 40 years
old, their eyes are unable to focus at normal reading distances
without reading glasses. Reduced illumination interferes with
focus depth and accommodation ability. Hardening of the lens
may also result in clouding of the lens (cataract formation).
Aviators with early cataracts may see a standard eye chart
clearly under normal daylight but have difficulty seeing under
bright light conditions. This problem is due to light scattering
as it enters the eye. This glare sensitivity is disabling under
certain circumstances. Glare disability, related to contrast
sensitivity, is the ability to detect objects against varying
shades of backgrounds. Other visual functions decline with
age and affect the aircrew member’s performance:
•
Dynamic acuity
•
Recovery from glare
•
Function under low illumination
•
Information processing
Vision in Flight
Figure 13-1. Effects of dimming cockpit lighting during night flight
to better see surrounding terrain.
13-2
The visual sense is especially important in collision
avoidance and depth perception. A pilot’s vision sensors are
the eyes, even though they are not perfect in the way they
function. Due to the structure of the human eye, illusions and
blindspots occur. The more pilots understand the eye and how
it functions, the easier it is to compensate for these illusions
and blindspots. Figure 13-3 shows the basic anatomy of the
Normal view
Astigmatic view
Figure 13-2. Example of a view that might be experienced by someone with astigmatism.
The rods and
cones (film) of
the retina are
the receptors
which record
the image and
transmit it
through the
optic nerve to
the brain for
interpretation.
Rods and
cones
Fovea
(All Cones)
Rod concentration
Lens
Iris
Optic nerve
Retina
PUPIL
CORNEA
The pupil (aperture) is the opening at
the center of the iris. The size of the
pupil is adjusted to control the amount
of light entering the eye.
Light passes through the cornea (the
transparent window on the front of the
eye) and then through the lens to
focus on the retina.
Figure 13-3. The human eye.
human eye and how it is like a camera. A camera is able
to focus on near and far objects by changing the distance
between the lens and the film. Objects can be seen clearly
at various distances because the shape of the eye’s lens is
changed automatically by small muscles.
Visual Acuity
Normal visual acuity, or sharpness, is 20/20. A value of
20/80 indicates that an individual reads at 20 feet the letters
that an individual with normal acuity (20/20) reads at 80
feet away. The human eye functions like a camera. It has
13-3
an instantaneous field of view, which is oval and typically
measures 120° vertically by 150° horizontally. When both
eyes are used for viewing, the overall field of vision measures
about 120° vertically by 200° horizontally.
The eye automatically adjusts for the light level experienced.
During night flight, the cockpit and instrument lights should
be as dim as possible. The eye can then adjust for the outside
lighting conditions (ambient lighting) to see outside. The
dimmer the inside lighting is, the better you can see outside.
The Eye
Vision is primarily the result of light striking a photosensitive
layer, called the retina, at the back of the eye. The retina is
composed of light-sensitive cones and rods. The cones in the
eye perceive an image best when the light is bright, while the
rods work best in low light. The pattern of light that strikes
the cones and rods is transmitted as electrical impulses by the
optic nerve to the brain where these signals are interpreted
as an image.
Cones
Cones are concentrated around the center of the retina. They
gradually diminish in number as the distance from the center
increases. Cones allow color perception by sensing red, blue,
and green light. Directly behind the lens, on the retina, is
a small, notched area called the fovea. This area contains
only a high concentration of cone receptors. The best vision
in daylight is obtained by looking directly at the object.
This focuses the image on the fovea, where detail is best
seen. The cones, however, do not function well in darkness,
which explains why color is not seen as vividly at night as
it is during the day.
Rods
Concentrated outside the fovea area, the rods are the dim
light and night receptors. The number of rods increases as the
distance from the fovea increases. Rods sense images only
in black and white. Because the rods are not located directly
behind the pupil, they are responsible for most peripheral
vision. Images that move are perceived more easily by the
rod areas than by the cones in the fovea. If you have ever
seen something move out of the corner of your eye, it was
most likely detected by rod receptors.
In low light, the cones lose much of their function, while
rods become more receptive. The eye sacrifices sharpness
for sensitivity. The ability to see an object directly in front
of you is reduced, and much depth perception is lost, as well
as judgment of size. The concentration of cones in the fovea
can make a night blindspot at the center of vision. How well
a person sees at night is determined by the rods in the eyes, as
well as the amount of light allowed into the eyes. The wider
the pupil is open at night, the better night vision becomes.
Night Vision
Diet and general physical health have an impact on how well
a person can see in the dark. Deficiencies in vitamins A and C
have been shown to reduce night acuity. Other factors, such
as carbon monoxide poisoning, smoking, alcohol, and certain
drugs can greatly decrease night vision. Lack of oxygen can
also decrease night vision as the eye requires more oxygen
per weight than any other part of the body.
Night Scanning
Good night visual acuity is needed for collision avoidance.
Night scanning, like day scanning, uses a series of short,
regularly spaced eye movements in 10° sectors. Unlike
day scanning, however, off-center viewing is used to
focus objects on the rods rather than the fovea blindspot.
[Figure 13-4] When looking at an object, avoid staring at
it too long. If staring at an object without moving the eyes,
the retina becomes accustomed to the light intensity and the
image begins to fade. To keep it clearly visible, new areas
in the retina must be exposed to the image. Small, circular
eye movements help eliminate the fading. Also, move the
eyes more slowly from sector to sector than during the day
to prevent blurring.
FOCAL POINTS
X
10°
X 10°
Observer
X 10°
10°
X
Figure 13-4. Off-center vision technique.
13-4
Once a target is detected in the peripheral
field of dark-adapted vision, aircrews
maintain continual surveillance by using
the off-center vision technique. They look
10 degrees above, below, or to either side
of the target, viewing it no longer than two
to three seconds at each position.
During daylight, objects can be perceived at a great distance
with good detail. At night, range is limited and detail is poor.
Objects along the flight path can be more readily identified at
night when pilots use the proper techniques to scan the terrain.
To scan effectively, pilots look from right to left or left to
right. They should begin scanning at the greatest distance
at which an object can be perceived (top) and move inward
toward the position of the aircraft (bottom). Figure 13-5
shows this scanning pattern. Because the light-sensitive
elements of the retina are unable to perceive images that are
in motion, a stop-turn-stop-turn motion should be used. For
each stop, an area about 30 degrees wide should be scanned.
This viewing angle includes an area about 250 meters wide at
a distance of 500 meters. The duration of each stop is based
on the degree of detail that is required, but no stop should
last more than two or three seconds. When moving from one
viewing point to the next, pilots should overlap the previous
field of view by 10 degrees. This scanning technique allows
greater clarity in observing the periphery. Other scanning
techniques, as illustrated in Figure 13-6, may be developed
to fit the situation.
10°
1
2
4
3
Figure 13-5. Scanning pattern.
3 seconds
3 seconds
3 seconds
6 seconds
on
se
c
4
ds
on
c
se
4 seconds
6 seconds
ds
4
6 seconds
4 seconds
6 seconds
6 seconds
3 seconds
3 seconds
3 seconds
Figure 13-6. Night vision.
13-5
Obstruction Detection
Obstructions having poor reflective surfaces, such as wires
and small tree limbs, are difficult to detect. The best way to
locate wires is by looking for the support structures. However,
pilots should review the most current hazard maps with
known wire locations before night flights.
Aircraft Lighting
In order to see other aircraft more clearly, regulations require
that all aircraft operating during the night hours have special
lights and equipment. The requirements for operating at night
are found in Title 14 of the Code of Federal Regulations (14
CFR) part 91. In addition to aircraft lighting, the regulations
also provide a definition of night flight in accordance with
14 CFR part 91, currency requirements, fuel reserves, and
necessary electrical systems.
Position lights enable a pilot to locate another aircraft, as
well as help determine its direction of flight. The approved
aircraft lights for night operations are a green light on the
right cabin side or wingtip, a red light on the left cabin side
or wingtip, and a white position light on the tail. In addition,
flashing aviation red or white anticollision lights are required
for night flights. These flashing lights can be in a number
of locations, but are most commonly found on the top and
bottom of the cabin.
Figure 13-7 shows examples of aircraft lighting. By
interpreting the position lights on other aircraft, the pilot in
aircraft 3 can determine whether the aircraft is flying in the
opposite direction or is on a collision course. If a red position
light is seen to the right of a green light, such as shown by
aircraft 1, it is flying toward aircraft 3. A pilot should watch
this aircraft closely and be ready to change course. Aircraft 2,
on the other hand, is flying away from aircraft 3, as indicated
by the white position light.
Visual Illusions
Illusions give false impressions or misconceptions of actual
conditions; therefore, pilots must understand the type of
illusions that can occur and the resulting disorientation.
Although the visual system is the most reliable of the senses,
some illusions can result from misinterpreting what is seen;
what is perceived is not always accurate. Even with the
references outside the cockpit and the display of instruments
inside, pilots must be on guard to interpret information
correctly.
Relative-Motion Illusion
Relative motion is the falsely perceived self-motion in
relation to the motion of another object. The most common
example is as follows. An individual in a car is stopped at a
traffic light and another car pulls alongside. The individual
that was stopped at the light perceives the forward motion
of the second car as his or her own motion rearward. This
results in the individual applying more pressure to the brakes
unnecessarily. This illusion can be encountered during flight
in situations such as formation flight, hover taxi, or hovering
over water or tall grass.
Confusion With Ground Lights
Confusion with ground lights occurs when a pilot mistakes
ground lights for stars. The pilot can place the helicopter
in an extremely dangerous flight attitude if he or she aligns
it with the wrong lights. In Figure 13-8A, the helicopter is
aligned with a road and not with the horizon. Isolated ground
lights can appear as stars and could lead to the illusion that
the helicopter is in a nose-high attitude.
When no stars are visible because of overcast conditions,
unlighted areas of terrain can blend with the dark overcast to
create the illusion that the unlighted terrain is part of the sky
in Figure 13-8B. In this illusion, the shoreline is mistaken for
the horizon. In an attempt to correct for the apparent nosehigh attitude, a pilot may lower the collective and attempt
to fly “beneath the shore.” This illusion can be avoided by
referencing the flight instruments and establishing a true
horizon and attitude.
Figure 13-7. Aircraft position lights.
13-6
Reversible Perspective Illusion
At night, an aircraft or helicopter may appear to be moving
away when it is actually approaching. If the pilot of each
aircraft has the same assumption, and the rate of closure is
significant, by the time each pilot realizes his or her own
error in assumption, it may be too late to avoid a mishap.
This illusion is called reversible perspective, and is often
experienced when a pilot observes another aircraft or
Stars
Overcast Sky
Ground Lights
Ocean
20
20
I0
I0
20
STBY PWR
20
20
I0
I0
I
I0
I0
20
20
STBY PWR
TEST
A
I0
II0
20
TEST
B
Figure 13-8. At night, the horizon may be hard to discern due to dark terrain and misleading light patterns on the ground.
helicopter flying a parallel course. To determine the direction
of flight, the pilot should observe the other aircraft’s position
lights. Remember the following: red on right returning; that
is, if an aircraft is seen with the red position light on the right
and the green position light on the left, the observed aircraft
is traveling in the opposite direction.
Flicker Vertigo
Flicker vertigo is technically not an illusion; however, as
most people are aware from personal experience, viewing
a flickering light can be both distracting and annoying.
Flicker vertigo may be created by helicopter rotor blades or
airplane propellers interrupting direct sunlight at a rate of 4
to 20 cycles per second. Flashing anticollision strobe lights,
especially while the aircraft is in the clouds, can also produce
this effect. One should also be aware that photic stimuli at
certain frequencies could produce seizures in those rare
individuals who are susceptible to flicker-induced epilepsy.
Night Flight
The night flying environment and the techniques used when
flying at night, depend on outside conditions. Flying on a
bright, clear, moonlit evening when the visibility is good and
the wind is calm is not much different from flying during the
day. However, if flying on an overcast night over a sparsely
populated area, with few or no outside lights on the ground,
the situation is quite different. Visibility is restricted, so be
more alert in steering clear of obstructions and low clouds.
Options are also limited in the event of an emergency, as it
is more difficult to find a place to land and determine wind
direction and speed. At night, rely more heavily on the aircraft
systems, such as lights, flight instruments, and navigation
equipment. As a precaution, if visibility is limited or outside
references are inadequate, strongly consider delaying the
flight until conditions improve, unless proper instrument
flight training has been received and the helicopter has the
appropriate instrumentation and equipment.
Preflight
Aircraft preflight inspection is a critical aspect of flight safety.
It must comply with the appropriate rotorcraft flight manual.
Preflight should be scheduled as early as possible in the
flight planning sequence, preferably during daylight hours,
allowing time for maintenance assistance and correction. If
a night preflight is necessary, a flashlight with an unfiltered
lens (white light) should be used to supplement lighting. Oil
and hydraulic fluid levels and leaks are difficult to detect with
a blue-green or red lens. Windscreens are checked ensuring
they are clean and relatively free of scratches. Slight scratches
are acceptable for day flight but may not be for night flight.
The search light or landing light should be positioned for
the best possible illumination during an emergency descent.
Careful attention must be paid to the aircraft electrical system.
In helicopters equipped with fuses, a spare set is required
by regulation, and common sense, so make sure they are on
board. If the helicopter is equipped with circuit breakers,
check to see that they are not tripped. A tripped circuit breaker
may be an indication of an equipment malfunction and should
be left for maintenance to troubleshoot.
All aircraft operating between sunset and sunrise are required
to have operable navigation (position) lights. Turn these lights
on during the preflight to inspect them visually for proper
operation. Between sunset and sunrise, these lights must be
on any time the helicopter is operating.
All recently manufactured aircraft certificated for night flight
must have an anticollision light that makes the aircraft more
visible to other pilots. This light is either a red or white
13-7
flashing light and may be in the form of a rotating beacon
or a strobe. While anticollision lights are required for night
visual flight rules (VFR) flights, they may be turned off any
time they create a distraction for the pilot.
One of the first steps in preparation for night flight is
becoming thoroughly familiar with the helicopter’s cockpit,
instrumentation, and control layout. It is recommended that
a pilot practice locating each instrument, control, and switch,
both with and without cabin lights. Since the markings on
some switches and circuit breaker panels may be difficult to
read at night, be able to locate and use these devices, and
read the markings in poor light conditions. Before starting
the engine, make sure all necessary equipment and supplies
needed for the flight, such as charts, notepads, and flashlights,
are accessible and ready for use.
Cockpit Lights
Check all interior lights with special attention to the
instrument and panel lights. The panel lighting can usually
be controlled with a rheostat or dimmer switch, allowing
the pilot to adjust the intensity. If a particular light is too
bright or causes reflection or glare off the windshield, it
should be adjusted or turned off. As ambient level decreases
from twilight to darkness, intensity of the cockpit lights is
reduced to a low, usable intensity level that reduces any glare
or reflection off the windshield. The light level should be
adjusted to as close to the ambient light level as possible. A
flashlight, with red or blue-green lens filter, or map light can
supplement the available light in the cockpit. Always carry a
flashlight with fresh batteries to provide an alternate source
of light if the interior lights malfunction. If an existing map/
utility light is used, it should be hand held or remounted to
a convenient location. In order to retain night adaptation
use low level light when using your checklist. Brief you
passengers in the importance of light discipline during night
flight so the pilot is not blinded and loses dark adaptation.
When operating at an unfamiliar airport at night, ask for
instructions or advice concerning local conditions, so as
to avoid taxiing into areas of construction, or unlighted,
unmarked obstructions. Ground controllers or UNICOM
operators are usually cooperative in furnishing this type of
information.
Takeoff
Before takeoff, make sure that there is a clear, unobstructed
takeoff path. At airports, this is accomplished by taking off
over a runway or taxi way, however, if operating off-airport,
pay more attention to the surroundings. Obstructions may
also be difficult to see if taking off from an unlighted area.
Once a suitable takeoff path is chosen, select a point down
the takeoff path to use for directional reference. The landing
light should be positioned in order to illuminate the tallest
obstacles in the takeoff path. During a night takeoff, notice
a lack of reliable outside visual references after becoming
airborne. This is particularly true at small airports and offairport landing sites located in sparsely populated areas.
To compensate for the lack of outside references, use the
available flight instruments as an aid. Check the altimeter and
the airspeed indicator to verify the proper climb attitude. An
attitude indicator, if installed, can enhance attitude reference.
The first 500 feet of altitude after takeoff is considered
to be the most critical period in transitioning from the
comparatively well-lit airport or heliport into what sometimes
appears to be total darkness. A takeoff at night is usually an
“altitude over airspeed” maneuver, meaning a pilot most
likely performs a nearly maximum performance takeoff. This
improves the chances for obstacle clearance and enhances
safety.
Engine Starting and Rotor Engagement
Use extra caution when starting the engine and engaging the
rotors, especially in dark areas with little or no outside lights.
In addition to the usual call of “clear,” turn on the position
and anticollision lights. If conditions permit, also turn the
landing light on momentarily to help warn others that the
engine is about to start and engage the rotors.
En Route Procedures
In order to provide a higher margin of safety, it is
recommended that a cruising altitude somewhat higher than
normal be selected. There are three reasons for this. First,
a higher altitude gives more clearance between obstacles,
especially those that are difficult to see at night, such as high
tension wires and unlighted towers. Second, in the event of
an engine failure, there is more time to set up for a landing
and the greater gliding distance gives more options for a safe
landing. Third, radio reception is improved, particularly if
using radio aids for navigation.
Taxi Technique
Landing lights usually cast a beam that is narrow and
concentrated ahead of the helicopter, so illumination to the
side is minimal. Therefore, slow the taxi at night, especially
in congested ramp and parking areas. Some helicopters have
a hover light in addition to a landing light, which illuminates
a larger area under the helicopter.
During preflight planning, it is recommended that a route of
flight that is within reach of an airport, or any safe landing
site, be selected when possible. It is also recommended
that pilots fly as close as possible to a populated or lighted
area, such as a highway or town. Not only does this offer
more options in the event of an emergency, but also makes
navigation a lot easier. A course comprised of a series of
13-8
slight zigzags to stay close to suitable landing sites and
well-lit areas, only adds a little more time and distance to an
otherwise straight course.
In the event of a forced landing at night, use the same
procedure recommended for day time emergency landings.
If available, turn on the landing light during the final descent
to help in avoiding obstacles along the approach path.
Collision Avoidance at Night
Because the quantity and quality of outside visual references
are greatly reduced, a pilot tends to focus on a single point or
instrument, making him or her less aware of the other traffic
around. Make a special effort to devote enough time to scan
for traffic. As discussed previously in the chapter, effective
scanning is accomplished with a series of short, regularly
spaced eye movements that bring successive areas of the
sky into the central visual field. Each movement should not
exceed 10 degrees, and each area should be observed for at
least 1 second to enable detection. If the pilot detects a dimly
lit object in a certain direction, the pilot should not look
directly at the object, but scan the area adjacent to it, called
off-center viewing. This will decrease the chances of fixating
on the light and allow focusing more on the objects (e.g.,
tower, aircraft, ground lights). Short stops of a few seconds
in duration in each scan will help to detect the light and its
movement. A pilot can determine another aircraft’s direction
of flight by interpreting the position and anticollision lights,
as previously described. When scanning, pilots should also
remember to move their heads, not just their eyes. Physical
obstructions can cover a considerable amount of sky, and
the area can easily be uncovered by a small head movement.
Approach and Landing
Night approaches and landings do have some advantages over
daytime approaches, as the air is generally smoother and the
disruptive effects of turbulence and excessive crosswinds are
often absent. However, there are a few special considerations
and techniques that apply to approaches at night. For example,
when landing at night, especially at an unfamiliar airport,
make the approach to a lighted runway and then use the
taxiways to avoid unlighted obstructions or equipment.
Carefully controlled studies have revealed that pilots have
a tendency to make lower approaches at night than during
the day. This is potentially dangerous as there is a greater
chance of hitting an obstacle, such as an overhead wire or
fence, that is difficult to see. It is good practice to make
steeper approaches at night, increasing the probability of
clearing obstacles. Monitor altitude and rate of descent using
the altimeter.
Another pilot tendency during night flight is to focus too
much on the landing area and not pay enough attention to
airspeed. If too much airspeed is lost, a settling-with-power
condition may result. Maintain the proper attitude during
the approach, and ensure that you keep some forward
airspeed and movement until close to the ground. Outside
visual references for airspeed and rate of closure may not be
available, especially when landing in an unlit area, so pay
special attention to the airspeed indicator.
Although the landing light is a helpful aid when making night
approaches, there is an inherent disadvantage. The portion
of the landing area illuminated by the landing light seems
higher than the dark area surrounding it. This effect can
cause a pilot to terminate the approach at an altitude that is
too high, which may result in a settling-with-power condition
and a hard landing.
Illusions Leading to Landing Errors
Various surface features and atmospheric conditions
encountered in landing can create illusions of incorrect height
above and distance from the runway threshold. Landing errors
from these illusions can be prevented by anticipating them
during approaches, conducting an aerial visual inspection of
unfamiliar airports before landing, using electronic glideslope
or VASI systems when available, and maintaining optimum
proficiency in landing procedures.
Featureless Terrain Illusion
An absence of ground features, as when landing over water,
darkened areas, and terrain made featureless by snow, can
create the illusion that the aircraft is at a higher altitude than
it actually is. The pilot who does not recognize this illusion
will fly a lower approach.
Atmospheric Illusions
Rain on the windscreen can create the illusion of greater
height, and atmospheric haze can create the illusion of being
at a greater distance from the runway. The pilot who does not
recognize these illusions flies a lower approach. Penetration
of fog can create the illusion of pitching up. The pilot who
does not recognize this illusion steepens the approach, often
quite abruptly.
Ground Lighting Illusions
Lights along a straight path, such as a road, and even lights
on moving trains can be mistaken for runway and approach
lights. Bright runway and approach lighting systems,
especially where few lights illuminate the surrounding
terrain, may create the illusion of less distance to the runway.
13-9
The pilot who does not recognize this illusion flies a higher
approach. Conversely, the pilot overflying terrain which has
few lights to provide height cues may make a lower than
normal approach.
Helicopter Night VFR Operations
While ceiling and visibility significantly affect safety in night
VFR operations, lighting conditions also have a profound
effect on safety. Even in conditions in which visibility and
ceiling are determined to be visual meteorological conditions,
the ability to discern unlit or low contrast objects and terrain
at night may be compromised. The ability to discern these
objects and terrain is referred to as the “seeing condition,”
and is related to the amount of natural and manmade lighting
available, and the contrast, reflectivity, and texture of
surface terrain and obstruction features. In order to conduct
operations safely, seeing conditions must be accounted for in
the planning and execution of night VFR operations.
Night VFR seeing conditions can be described by identifying
high lighting conditions and low lighting conditions.
High lighting conditions exist when one of two sets of
conditions are present:
1.
The sky cover is less than broken (less than 5⁄8 cloud
cover), the time is between the local moon rise and
moon set, and the lunar disk is at least 50 percent
illuminated; or
2.
The aircraft is operated over surface lighting that, at
least, provides lighting of prominent obstacles, the
identification of terrain features (shorelines, valleys,
hills, mountains, slopes) and a horizontal reference
by which the pilot may control the helicopter. For
example, this surface lighting may be the result of:
13-10
a.
Extensive cultural lighting (manmade, such as a
built-up area of a city),
b.
Significant reflected cultural lighting (such as the
illumination caused by the reflection of a major
metropolitan area’s lighting reflecting off a cloud
ceiling), or
c.
Limited cultural lighting combined with a
high level of natural reflectivity of celestial
illumination, such as that provided by a surface
covered by snow or a desert surface.
Low lighting conditions are those that do not meet the high
lighting conditions requirements.
Some areas may be considered a high lighting environment
only in specific circumstances. For example, some surfaces,
such as a forest with limited cultural lighting, normally
have little reflectivity, requiring dependence on significant
moonlight to achieve a high lighting condition. However,
when that same forest is covered with snow, its reflectivity
may support a high lighting condition based only on starlight.
Similarly, a desolate area, with little cultural lighting, such
as a desert, may have such inherent natural reflectivity that it
may be considered a high lighting conditions area regardless
of season, provided the cloud cover does not prevent starlight
from being reflected from the surface. Other surfaces, such
as areas of open water, may never have enough reflectivity
or cultural lighting to ever be characterized as a high lighting
area.
Through the accumulation of night flying experience in a
particular area, the pilot develops the ability to determine,
prior to departure, which areas can be considered supporting
high or low lighting conditions. Without that pilot experience,
low lighting considerations should be applied by pilots for
both preflight planning and operations until high lighting
conditions are observed or determined to be regularly
available.
Chapter Summary
Knowledge of the basic anatomy and physiology of the eye
is helpful in the study of helicopter night operations. Adding
to that knowledge a study of visual illusions gives the pilot
ways to overcome those illusions. Techniques for preflight,
engine start-up, collision avoidance, and night approach and
landings help teach the pilot safer ways to conduct flight at
night. More detailed information on the subjects discussed
in this chapter is available in the Aeronautical Information
Manual (AIM) and online at www.faa.gov.
Chapter 14
Effective Aeronautical
Decision-Making
Introduction
The accident rate for helicopters has traditionally been higher
than the accident rate of fixed-wing aircraft, probably due to
the helicopter’s unique capabilities to fly and land in more
diverse situations than fixed-wing aircraft and pilot attempts
to fly the helicopter beyond the limits of his or her abilities or
beyond the capabilities of the helicopter. With no significant
improvement in helicopter accident rates for the last 20 years,
the Federal Aviation Administration (FAA) has joined with
various members of the helicopter community to improve
the safety of helicopter operations.
According to National Transportation Safety Board (NTSB)
statistics, approximately 80 percent of all aviation accidents
are caused by pilot error, the human factor. Many of
these accidents are the result of the failure of instructors
to incorporate single-pilot resource management (SRM)
and risk management into flight training instruction of
aeronautical decision-making (ADM).
SRM is defined as the art of managing all the resources (both
on board the aircraft and from outside sources) available to a
pilot prior to and during flight to ensure a successful flight.
When properly applied, SRM is a key component of ADM.
Additional discussion includes integral topics such as, the
concepts of risk management, workload or task management,
situational awareness, controlled flight into terrain (CFIT)
awareness, and automation management.
14-1
ADM is all about learning how to gather information, analyze
it, and make decisions. It helps the pilot accurately assess
and manage risk and make accurate and timely decisions.
Although the flight is coordinated by a single person, the use
of available resources, such as air traffic control (ATC) and
flight service stations (FSS)/automated flight service stations
(AFSS), replicates the principles of CRM.
References on SRM and ADM include:
•
FAA-H-8083-2, Risk Management Handbook.
•
Aeronautical Information Manual (AIM).
•
Advisory Circular (AC) 60-22, Aeronautical Decision
Making, which provides background information
about ADM training in the general aviation (GA)
environment.
•
FAA-H-8083-25, Pilot’s Handbook of Aeronautical
Knowledge.
Aeronautical Decision-Making (ADM)
Making good choices sounds easy enough. However,
there are a multitude of factors that come into play when
these choices, and subsequent decisions, are made in the
aeronautical world. Many tools are available for pilots to
become more self aware and assess the options available,
along with the impact of their decision. Yet, with all the
available resources, accident rates are not being reduced. Poor
decisions continue to be made, frequently resulting in lives
being lost and/or aircraft damaged or destroyed. The Risk
Management Handbook discusses ADM and SRM in detail
and should be thoroughly read and understood.
While progress is continually being made in the advancement
of pilot training methods, aircraft equipment and systems, and
services for pilots, accidents still occur. Historically, the term
“pilot error” has been used to describe the causes of these
accidents. Pilot error means an action or decision made by
the pilot was the cause of, or a contributing factor that led to,
the accident. This definition also includes the pilot’s failure to
make a decision or take action. From a broader perspective,
the phrase “human factors related” more aptly describes these
accidents since it is usually not a single decision that leads
to an accident, but a chain of events triggered by a number
of factors. [Figure 14-1]
The poor judgment chain, sometimes referred to as the “error
chain,” is a term used to describe this concept of contributing
factors in a human factors related accident. Breaking one
link in the chain is often the only event necessary to change
the outcome of the sequence of events. The following is an
example of the type of scenario illustrating the poor judgment
chain.
Scenario
An emergency medical services (EMS) helicopter pilot is
nearing the end of his shift when he receives a request for a
patient pickup at a roadside vehicle accident. The pilot has
started to feel the onset of a cold; his thoughts are on getting
home and getting a good night’s sleep. After receiving the
request, the pilot checks the accident location and required
flightpath to determine if he has time to complete the flight
to the scene, then on to the hospital before his shift expires.
The pilot checks the weather and determines that, although
thunderstorms are approaching, the flight can be completed
prior to their arrival.
Task Load
High
Low
Takeo
ff
Time
ents
ht
Pilot
equirem
Preflig
s
e
i
t
i
l
i
b
Capa
Appro
ach &
Task R
Cruise
Landin
g
Figure 14-1. The pilot has a limited capacity of doing work and handling tasks, meaning there is a point at which the tasking exceeds
the pilot’s capability. When this happens, either tasks are not done properly or some are not done at all.
14-2
The pilot and on-board medical crews depart the home
location and arrive overhead, at the scene of the vehicular
accident. The pilot is not comfortable with the selected
landing area due to tall trees in all quadrants of the confined
area. The pilot searches for a secondary landing area. Unable
to find one nearby, the pilot then returns to the initial landing
area and decides he can make it work.
After successfully landing the aircraft, he is told that there
will be a delay before the patient is loaded because more time
is needed to extricate the patient from the wreckage. Knowing
his shift is nearly over, the pilot begins to feel pressured to
“hurry up” or he will require an extension for his duty day.
After 30 minutes, the patient is loaded and the pilot ensures
everyone is secure. He notes that the storm is now nearby and
that winds have picked up considerably. The pilot thinks, “No
turning back now, the patient is on board and I’m running out
of time.” The pilot knows he must take off almost vertically
to clear the obstacles, and chooses his departure path based
on the observed wind during landing. Moments later, prior to
clearing the obstacles, the aircraft begins an uncontrollable
spin and augers back to the ground, seriously injuring all on
board and destroying the aircraft.
What could the pilot have done differently to break this
error chain? More important—what would you have done
differently? By discussing the events that led to this accident,
you should develop an understanding of how a series of
judgmental errors contributed to the final outcome of this
flight.
For example, the pilot’s decision to fly the aircraft knowing
that the effects of an illness were present was the initial
contributing factor. The pilot was aware of his illness, but,
was he aware of the impact of the symptoms—fatigue,
general uneasy feeling due to a slight fever, perhaps?
Next, knowing the shift was about to end, the pilot based his
time required to complete the flight on ideal conditions, and
did not take into consideration the possibility of delays. This
led to a feeling of being time limited.
Even after determining the landing area was unsuitable, the
pilot forced the landing due to time constraints. At any time
during this sequence, the pilot could have aborted the flight
rather than risk crew lives. Instead, the pilot became blinded
by a determination to continue.
After landing, and waiting 30 minutes longer than planned,
the pilot observed the outer effects of the thunderstorm, yet
still attempted to depart. The pilot dispelled any available
options by thinking the only option was to go forward;
however, it would have been safer to discontinue the flight.
Using the same departure path selected under different wind
conditions, the pilot took off and encountered winds that
led to loss of aircraft control. Once again faced with a selfimposed time constraint, the pilot improperly chose to depart
the confined area. The end result: instead of one patient to
transport by ground (had the pilot aborted the flight at any
point), there were four patients to be transported.
On numerous occasions leading to and during the flight, the
pilot could have made effective decisions that could have
prevented this accident. However, as the chain of events
unfolded, each poor decision left him with fewer options.
Making sound decisions is the key to preventing accidents.
Traditional pilot training emphasizes flying skills, knowledge
of the aircraft, and familiarity with regulations. SRM and
ADM training focus on the decision-making process and the
factors that affect a pilot’s ability to make effective choices.
Trescott Tips
Max Trescott, Master CFI and Master Ground Instructor and
winner of the 2008 CFI of the year, has published numerous
safety tips that every pilot should heed. He believes that
the word “probably” should be purged from our flying
vocabulary. Mr. Trescott contends that “probably” means
we’ve done an informal assessment of the likelihood of an
event occurring and have assigned a probability to it. He
believes the term implies that we believe things are likely
to work out, but there’s some reasonable doubt in our mind.
He further explains that if you ever think that your course of
action will “probably work out,” you need to choose a new
option that you know will work out.
Another safety tip details the importance of accumulating
flight hours in one specific airframe type. He explains that
“statistics have shown that accidents are correlated more with
the number of hours of experience a pilot has in a particular
aircraft model and not with his or her total number of flight
hours. Accidents tend to decrease after a pilot accumulates
at least 100 hours of experience in the aircraft he or she is
flying. Thus when learning to fly or transitioning into a new
model, your goal should be to concentrate your flying hours
in that model.” He suggests waiting until you reach 100 hours
of experience in one particular model before attempting a
dual rating with another model. In addition, if you only fly a
few hours per year, maximize your safety by concentrating
those hours in just one aircraft model.
14-3
The third safety tip that is well worth mentioning is what
Mr. Trescott calls “building experience from the armchair”.
Armchair flying is simply closing your eyes and mentally
practicing exactly what you do in the aircraft. This is an
excellent way to practice making radio calls, departures,
approaches and even visualizing the parts and pieces of the
aircraft. This type of flying does not cost a dime and will
make you a better prepared and more proficient pilot.
All three of Max Trescott’s safety tips incorporate the ADM
process and emphasize the importance of how safety and
good decision-making is essential to aviation.
The Decision-Making Process
An understanding of the decision-making process provides
a pilot with a foundation for developing ADM skills. Some
situations, such as engine failures, require a pilot to respond
immediately using established procedures with little time
for detailed analysis. Called automatic decision-making,
it is based upon training, experience, and recognition.
Traditionally, pilots have been well trained to react to
emergencies, but are not as well prepared to make decisions
that require a more reflective response when greater analysis
is necessary. They often overlook the phase of decisionmaking that is accomplished on the ground: the preflight,
flight planning, performance planning, weather briefing, and
weight/center of gravity configurations. Thorough and proper
completion of these tasks provides increased awareness and
a base of knowledge available to the pilot prior to departure
and once airborne. Typically during a flight, a pilot has time
to examine any changes that occur, gather information, and
assess risk before reaching a decision. The steps leading to
this conclusion constitute the decision-making process.
Defining the Problem
Defining the problem is the first step in the decision-making
process and begins with recognizing that a change has
occurred or that an expected change did not occur. A problem
is perceived first by the senses, then is distinguished through
insight (self-awareness) and experience. Insight, experience,
and objective analysis of all available information are used to
determine the exact nature and severity of the problem. One
critical error that can be made during the decision-making
process is incorrectly defining the problem.
While going through the following example, keep in mind
what errors lead up to the event. What planning could have
been completed prior to departing that may have led to
avoiding this situation? What instruction could the pilot have
had during training that may have better prepared the pilot
for this scenario? Could the pilot have assessed potential
problems based on what the aircraft “felt like” at a hover?
14-4
All these factors go into recognizing a change and the timely
response.
While doing a hover check after picking up firefighters at
the bottom of a canyon, a pilot realized that she was only
20 pounds under maximum gross weight. What she failed
to realize was that the firefighters had stowed some of their
heaviest gear in the baggage compartment, which shifted
the center of gravity (CG) slightly behind the aft limits.
Since weight and balance had never created any problems
for her in the past, she did not bother to calculate CG and
power required. She did try to estimate it by remembering
the figures from earlier in the morning at the base camp. At a
5,000-foot density altitude (DA) and maximum gross weight,
the performance charts indicated the helicopter had plenty of
excess power. Unfortunately, the temperature was 93 °F and
the pressure altitude at the pickup point was 6,200 feet (DA
= 9,600 feet). Since there was enough power for the hover
check, the pilot decided there was sufficient power to take off.
Even though the helicopter accelerated slowly during the
takeoff, the distance between the helicopter and the ground
continued to increase. However, when the pilot attempted to
establish the best rate of climb speed, the nose tended to pitch
up to a higher-than-normal attitude, and the pilot noticed that
the helicopter was not gaining enough altitude in relation to
the canyon wall approximately 200 yards ahead.
Choosing a Course of Action
After the problem has been identified, a pilot must evaluate
the need to react to it and determine the actions to take to
resolve the situation in the time available. The expected
outcome of each possible action should be considered and
the risks assessed before a pilot decides on a response to the
situation.
The pilot’s first thought was to pull up on the collective and
pull back on the cyclic. After weighing the consequences of
possibly losing rotor revolutions per minute (rpm) and not
being able to maintain the climb rate sufficiently to clear the
canyon wall, which is now only a hundred yards away, she
realized the only course was to try to turn back to the landing
zone on the canyon floor.
Implementing the Decision and Evaluating the
Outcome
Although a decision may be reached and a course of action
implemented, the decision-making process is not complete.
It is important to think ahead and determine how the decision
could affect other phases of the flight. As the flight progresses,
a pilot must continue to evaluate the outcome of the decision
to ensure that it is producing the desired result.
As the pilot made the turn to the downwind, the airspeed
dropped nearly to zero, and the helicopter became very
difficult to control. At this point, the pilot must increase
airspeed in order to maintain translational lift, but since the
CG was aft of limits, she needed to apply more forward cyclic
than usual. As she approached the landing zone with a high
rate of descent, she realized that she would be in a potential
settling-with-power situation if she tried to trade airspeed for
altitude and lost effective translational lift (ETL). Therefore,
it did not appear that she would be able to terminate the
approach in a hover. The pilot decided to make the shallowest
approach possible and perform a run-on landing.
Pilots sometimes have trouble not because of deficient basic
skills or system knowledge, but because of faulty decisionmaking skills. Although aeronautical decisions may appear
to be simple or routine, each individual decision in aviation
often defines the options available for the next decision the
pilot must make and the options (good or bad) it provides.
Therefore, a poor decision early in a flight can compromise
the safety of the flight at a later time. It is important to
make accurate and decisive choices because good decisionmaking early in an emergency provide greater latitude for
later options.
Decision-Making Models
The decision-making process normally consists of several
steps before a pilot chooses a course of action. A variety
of structured frameworks for decision-making provide
assistance in organizing the decision process. These models
include but are not limited to the 5P (Plan, Plane, Pilot,
Passengers, Programming), the OODA Loop (Observation,
Orientation, Decision, Action), and the DECIDE (Detect,
Estimate, Choose, Identify, Do, and Evaluate) models.
[Figure 14-2] All these models and their variations are
discussed in detail in the Pilot’s Handbook of Aeronautical
Knowledge section covering aeronautical decision-making.
Problem-Based Learning
Scenario-Based Training
Learner-Centered Grading
facilitate development of
Higher-Order Thinking Skills (HOTS)
Aeronautical Decision-Making
ADM is a systematic approach to
the mental process of evaluating
a given set of circumstances and
determining the best course
of action.
Single-Pilot Resource Management
5P Model: Plan, plane, pilot, passengers, programming
Incorporates the elements of
Risk
Management
g
Task
Management
g
Information
Management
g
Automation
Management
g
Risk management is a
decision-making process
designed to identify hazards
systematically, assess the
degree of risk, and determine
the best course of action.
Task management is the
process pilots use to manage
the many concurrent tasks
involved in safely flying
an aircraft.
Information management is the
process pilots use to gather
pertinent information from all
appropriate sources.
Automation management is
the ability to control and
navigate an aircraft by
correctly managing its
automated systems.
3P Model
Perceive, Process, Perform
to identify, evaluate, and
mitigate hazards related to
Pilot
Aircraft
EnVironment
External Pressures
These elements combine to create and maintain
Situational Awareness
Situational awareness is the accurate perception and understanding of all the factors and conditions
within the four fundamental risk elements (pilot, aircraft, environment, external pressures).
Figure 14-2. Various models of decision-making are used in problem solving.
14-5
Whatever model is used, the pilot learns how to define the
problem, choose a course of action, implement the decision,
and evaluate the outcome. Remember, there is no one right
answer in this process; a pilot analyzes the situation in light
of experience level, personal minimums, and current physical
and mental readiness levels, and makes a decision.
Pilot Self-Assessment
The PIC of an aircraft is directly responsible for and is the
final authority for the operation of that aircraft. The list of PIC
responsibilities is long, and nothing should be overlooked. To
exercise those responsibilities effectively and make effective
decisions regarding the outcome of a flight, a pilot must have
an understanding of personal limitations. Pilot performance
from planning the flight to execution of the flight is affected
by many factors, such as health, experience, knowledge, skill
level, and attitude.
Exercising good judgment begins prior to taking the controls
of an aircraft. Often, pilots thoroughly check their aircraft
to determine airworthiness, yet do not evaluate their own
fitness for flight. Just as a checklist is used when preflighting
an aircraft, a personal checklist based on such factors as
experience, currency, and comfort level can help determine
if a pilot is prepared for a particular flight. Specifying when
refresher training should be accomplished and designating
weather minimums, which may be higher than those listed
in Title 14 of the Code of Federal Regulations (14 CFR) part
91, are elements that may be included on a personal checklist.
Over confidence can kill just as fast as inexperience. In
addition to a review of personal limitations, a pilot should
use the I’M SAFE checklist to further evaluate fitness for
flight. [Figure 14-3]
I’M SAFE CHECKLIST
ST
Illness—Do I have anyy symptoms?
y p
Medication—Have I been takingg prescription
p
p ion or
over-the-counter drugs?
g
Stress—Am I under ppsychological
y
g
pressure
p
e from
the jjob? Worried about financial matters,, health
ealth
h
problems,, or familyy discord?
p
Alcohol—Have I been drinkingg within 8 hours?
ho
ours?
Within 24 hours?
Fatigue—Am
g
I tired and not adequately
eq
quatelyy rested?
ressted?
?
Emotion—Am I angry, depressed,
ess
ssed, or anxious?
anxiou
ous?
s?
?
Figure 14-3. I’M SAFE checklist.
14-6
Curiosity: Healthy or Harmful?
The roots of aviation are firmly based on curiosity. Where
would we be today had it not been for the dreams of Leonardo
da Vinci, the Wright Brothers, and Igor Sikorsky? They all
were infatuated with flight, a curiosity that led to the origins
of aviation. The tale of aviation is full of firsts: first flight, first
helicopter, first trans-Atlantic flight, and so on. But, along the
way there were many setbacks, fatalities, and lessons learned.
Today, we continue to learn and investigate the limits of
aviation. We’ve been to the moon, and soon beyond. Our
curiosity will continue to drive us to search for the next
challenge.
However, curiosity can also have catastrophic consequences.
Despite over 100 years of aviation practice, we still see
accidents that are caused by impaired judgment formed
from curious behavior. Pilots commonly seek to determine
the limits of their ability as well as the limits of the aircraft.
Unfortunately, too often this leads to mishaps with deadly
results. Inquisitive behavior must be harnessed and displayed
within personal and material limits.
Deadly curiosity may not seem as obvious to some as it is to
others. Simple thoughts such as, “Is visibility really as bad
as what the ATIS is reporting?” or “Will the 20 minute fuel
light really indicate only 20 minutes worth of fuel?” can lead
to poor decisions and disastrous outcomes.
Some aviators blatantly violate rules and aircraft limitations
without thinking through the consequences. “What
indications and change in flight characteristics will I see if
I fly this helicopter above its maximum gross weight?” or
“I’ve heard this helicopter can do aerobatic flight. Why is it
prohibited?” are examples of extremely harmful curiosity.
Even more astounding is their ignoring to the fact that the
damage potentially done to the aircraft will probably manifest
later in the aircraft’s life, affecting other crews. Spontaneous
excursions in aviation can be deadly.
Curiosity is natural, and promotes learning. Airmen should
abide by established procedures until proper and complete
hazard assessment and risk management can be completed.
The PAVE Checklist
As found in the Pilot’s Handbook of Aeronautical
Knowledge, the FAA has designed a personal minimums
checklist. To help pilots with self-assessment, which in turn
helps mitigate risk, the acronym PAVE divides the risks of
flight into four categories. For each category, think of the
applicability specific to helicopter operations:
•
•
•
•
Pilot (pilot in command)
-
Physical, emotional readiness.
-
Flight experience, recency, currency, total time
in type.
Aircraft
-
Is the helicopter capable of performing the task?
-
Can it carry the necessary fuel?
-
Does it provide adequate power margins for the
task to be accomplished?
-
Can it carry the weight and remain within CG?
-
Will there be external loads?
EnVironment
-
Helicopters are susceptible to the impact of
changing weather conditions.
-
How will the change in moderating temperatures
and DA affect performance?
-
Will controllability be jeopardized by winds,
terrain, and turbulence?
External pressures
-
Do not let the notion to accomplish “the mission”
override good judgment and safety.
-
Many jobs include time lines. How often do we
hear “time is money” or “time is wasting”? Don’t
sacrifice safety for an implied or actual need to
meet the deadline!
-
Do not allow yourself to feel pressured by
coworkers, family events, or friends.
Incorporated into preflight planning, the PAVE checklist
provides the pilot with a simple way to remember each
category to examine for risk prior to each flight. Once the
pilot identifies the risks of a flight, he or she needs to decide
whether the risk or combination of risks can be managed
safely and successfully. Remember, the PIC is responsible
for deciding about canceling the flight. If the pilot decides to
continue with the flight, he or she should develop strategies
to mitigate the risks.
One way to control risk is by setting personal minimums
for items in each risk category. Remember, these are limits
unique to an individual pilot’s current level of experience and
proficiency. They should be reevaluated periodically based
upon experience and proficiency.
Single-Pilot Resource Management
Many of the concepts utilized in CRM have been successfully
applied to single-pilot operations which led to the development
of SRM. Defined as the art and science of managing all the
resources (both on board the aircraft and from outside
resources) available to a single pilot (prior to and during
flight), SRM ensures the successful outcome of the flight. As
mentioned earlier, this includes risk management, situational
awareness, and CFIT awareness.
SRM training helps the pilot maintain situational awareness
by managing automation, associated control, and navigation
tasks. This enables the pilot to accurately assess hazards,
manage resulting risk potential, and make good decisions.
To make informed decisions during flight operations, a pilot
must be aware of the resources found both inside and outside
the cockpit. Since useful tools and sources of information may
not always be readily apparent, learning to recognize these
resources is an essential part of SRM training. Resources must
not only be identified, but a pilot must also develop the skills
to evaluate whether he or she has the time to use a particular
resource and the impact its use has upon the safety of flight.
If a pilot is flying alone into a confined area with no wind
sock or access to a current wind report, should that pilot pick
an approach path based on the direction of wind information
received from an earlier weather brief? Making an approach
into a confined area with a tailwind is a bad decision and can
be avoided. Prior to landing, the pilot should use outside
resources such a smoke, trees, and water on a pond to help
him or her accurately determine which direction the winds are
coming from. Pilots should never leave flying up to chance
and hope for the best. Many accidents could and should be
avoided by simply using the resources, internal and external
that are available.
Internal resources are found in the cockpit during flight. Since
some of the most valuable internal resources are ingenuity,
knowledge, and skill, a pilot can expand cockpit resources
immensely by improving these capabilities. This can be
accomplished by frequently reviewing flight information
publications, such as 14 CFR and the AIM, as well as by
pursuing additional training.
No other internal resource is more important than the pilot’s
ability to control the situation, thereby controlling the aircraft.
Helicopter pilots quickly learn that it is not possible to hover,
single pilot, and pick up the checklist, a chart, or publication
without endangering themselves, the aircraft, or those nearby.
14-7
Checklists are essential cockpit resources used to verify
the aircraft instruments and systems are checked, set, and
operating properly. They also ensure proper procedures
are performed if there is a system malfunction or inflight
emergency. Pilots at all levels of experience refer to
checklists. The more advanced the aircraft is, the more crucial
checklists are.
Without a doubt, problems began during the planning phase,
as the necessary resources were placed in the back of the
aircraft, unavailable to the pilot during flight. Additional
training with the available automated systems installed on
the helicopter would have expedited access to the necessary
information. What if they hadn’t been installed or were
inoperative?
Therefore, have a plan on how to use the checklist (and other
necessary publications) before you begin the flight. Always
control the helicopter first. When hovering in an airport
environment, the pilot can always land the aircraft to access
the checklist or a publication, or have a passenger assist with
holding items. There is nothing more unsettling than being in
flight and not having a well thought-out plan for managing
the necessary documents and data. This lack of planning
often leads to confusion, distractions and aircraft mishaps.
Next, a poor decision to continue towards the Class C airspace
was made. The pilot could have turned away from the Class
C airspace, removing himself from the situation until the
frequencies were entered and contact established. Remember,
when possible, choose an option that gives more time to
determine a course of action. Proper resource management
could have negated this airspace violation.
Another way to avoid a potentially complex and confusing
situation is to remove yourself from the situation. The
following is an example of how proper resource management
and removal from a situation are vital to safe flight.
A single pilot is conducting a helicopter cross-country flight.
He frequently goes to and is familiar with the final destination
airport. Weather is briefed to be well above the minimum
weather needed, but with isolated thunderstorms possible.
For the pilot, this is a routine run-of-the-mill flight. He has
done this many times before and has memorized the route,
checkpoints, the frequencies, fuel required and knows exactly
what to expect.
However, once within 30 miles of the destination airport
the pilot observes that weather is deteriorating and a
thunderstorm is nearby. The pilot assesses the situation and
determines the best course of action is to reroute to another
airport. The closest airport is an airport within Class C
airspace. At this point, the pilot realizes the publications with
the required alternate airport information are in the back of
the helicopter out of reach. Now what?
The pilot continues toward the alternate airport while
using the onboard equipment to access the information.
He struggles to obtain the information because he or she
is not thoroughly familiar with its operation. Finally, the
information is acquired and the pilot dials in the appropriate
alternate airfield information. Upon initial contact ARTCC
(Air Route Traffic Control Center) notifies the pilot that he
has entered the airspace without the required clearance; in
effect the pilot has violated airspace regulations.
Things have gone from bad to worse for him. When did the
trouble begin for this pilot and what options were available?
14-8
The example also demonstrates the need to have a thorough
understanding of all the equipment and systems in the
aircraft. As is often the case, the technology available today
is seldom used to its maximum capability. It is necessary to
become as familiar as possible with this equipment to utilize
all resources fully. For example, advanced navigation and
autopilot systems are valuable resources. However, if pilots
do not fully understand how to use this equipment, or they
rely on it so much they become complacent, the equipment
can become a detriment to safe flight.
Another internal resource is the FAA-approved rotorcraft
flight manual (RFM). [Figure 14-4] The RFM:
•
Must be on board the aircraft.
•
Is indispensable for accurate flight planning.
•
Plays a vital role in the resolution of inflight equipment
malfunctions.
ROBINSON R22
R OTORCRAFT
F LIGHT
M ANUAL
Figure 14-4. FAA-approved Rotorcraft Flying Manual (RFM).
Other valuable flight deck resources include current
aeronautical charts and publications, such as the Airport/
Facility Directory (A/FD).
As stated previously, passengers can also be a valuable
resource. Passengers can help watch for traffic and may
be able to provide information in an irregular situation,
especially if they are familiar with flying. Crew briefs to
passengers should always include some basic helicopter
terminology. For example, explain that in the event you ask
them if you are clear to hover to the right, their response
should be either “yes, you are clear to hover to the right” or
“no you are not clear.” A simple yes or no answer can be
ambiguous. A strange smell or sound may alert a passenger to
a potential problem. As PIC, a pilot should brief passengers
before the flight to make sure that they are comfortable
voicing any concerns.
Instruction that integrates Single-Pilot Resource Management
into flight training teaches aspiring pilots how to be more
aware of potential risks in flying, how to identify those
risks clearly, and how to manage them successfully. The
importance of integrating available resources and learning
effective SRM skills cannot be overemphasized. Ignoring
safety issues can have fatal results.
Risk Management
Risk management is a formalized way of dealing with
hazards. It is the logical process of weighing the potential
cost of risks from hazards against the possible benefits of
allowing those risks from hazards to stand unmitigated. It
is a decision-making process designed to identify hazards
systematically, assess the degree of risk, and determine the
best course of action. Once risks are identified, they must be
assessed. The risk assessment determines the degree of risk
(negligible, low, medium, or high) and whether the degree
of risk is worth the outcome of the planned activity. If the
degree of risk is “acceptable,” the planned activity may
then be undertaken. Once the planned activity is started,
consideration must then be given whether to continue. Pilots
must have preplanned, viable alternatives available in the
event the original flight cannot be accomplished as planned.
Two defining elements of risk management are hazard and
risk.
•
A hazard is a present condition, event, object, or
circumstance that could lead to or contribute to an
unplanned or undesired event, such as an accident.
It is a source of danger. For example, binding in the
antitorque pedals represents a hazard.
•
Risk is the future impact of a hazard that is not
controlled or eliminated. It is the possibility of loss
or injury. The level of risk is measured by the number
of people or resources affected (exposure), the extent
of possible loss (severity), and the likelihood of loss
(probability).
A hazard can be a real or perceived condition, event, or
circumstance that a pilot encounters. Learning how to identify
hazards, assess the degree of risk they pose, and determine the
best course of action is an important element of a safe flight.
Four Risk Elements
During each flight, decisions must be made regarding events
that involve interactions between the four risk elements—
the pilot in command (PIC), the aircraft, the environment,
and the operation. The decision-making process involves
an evaluation of each of these risk elements to achieve an
accurate perception of the flight situation. [Figure 14-5]
RISK ELEMENTS
Pilot
The pilot’s fitness to fly must
be evaluated, including competency in the helicopter,
currency, and flight experience.
Aircraft
The helicopter performance,
limitations, equipment, and
airworthiness must be determined.
Environment
Factors such as weather and
airport conditions must be
examined.
External Pressures
The purpose of the flight is a
factor that influences the pilot’s
decision on undertaking or
continuing the flight.
Situation
To maintain situational awareness, an accurate
perception must be attained of how the pilot, helicopter,
environment, and operation combine to affect the flight.
Figure 14-5. Risk elements to evaluate in decision-making.
14-9
One of the most important decisions that a PIC must make is
the go/no-go decision. Evaluating each of these risk elements
can help a pilot decide whether a flight should be conducted or
continued. In the following situations, the four risk elements
and how they affect decision-making are evaluated.
Pilot—A pilot must continually make decisions about
personal competency, condition of health, mental and
emotional state, level of fatigue, and many other variables.
A situation to consider: a pilot is called early in the morning
to make a long flight. With only a few hours of sleep and
congestion that indicates the possible onset of a cold, is that
pilot safe to fly?
Aircraft—A pilot frequently bases decisions to fly on
personal evaluations of the aircraft, such as its powerplant,
performance, equipment, fuel state, or airworthiness. A
situation to consider: en route to an oil rig an hour’s flight
from shore, having just passed the shoreline, the pilot notices
the oil temperature at the high end of the caution range.
Should the pilot continue out to sea or return to the nearest
suitable heliport/airport?
Environment—This encompasses many elements unrelated
to the pilot or aircraft. It can include such factors as weather,
ATC, navigational aids (NAVAID), terrain, takeoff and
landing areas, and surrounding obstacles. Weather is one
element that can change drastically over time and distance.
A situation to consider: a pilot is ferrying a helicopter crosscountry and encounters unexpected low clouds and rain in an
area of rising terrain. Does the pilot try to stay under them
and scud run, or turn around, stay in the clear, and obtain
current weather information?
External Pressures—The interaction between the pilot,
the aircraft, and the environment is greatly influenced by
the purpose of each flight operation. A pilot must evaluate
the three previous areas to decide on the desirability of
undertaking or continuing the flight as planned. It is worth
asking why the flight is being made, how critical it is to
maintain the schedule, and if the trip is worth the risks. A
situation to consider: a pilot is tasked to take some technicians
into rugged mountains for a routine survey in marginal
weather. Would it be preferable to wait for better conditions
to ensure a safe flight? How would the priorities change if a
pilot were tasked to search for cross-country skiers who had
become lost in deep snow and radioed for help?
Assessing Risk
It is important for a pilot to learn how to assess risk. Before a
pilot can begin to assess risk, he or she must first perceive the
hazard and attendant risk(s). In aviation, experience, training,
and education help a pilot learn how to spot hazards quickly
14-10
and accurately. During flight training, the instructor should
point out the hazards and attendant risks to help the student
pilot learn to recognize them.
Once a hazard is identified, determining the probability
and severity of an accident (level of risk associated with it)
becomes the next step. For example, the hazard of binding
in the antitorque pedals poses a risk only if the helicopter is
flown. If the binding leads to a loss of directional control,
the risk is high that it could cause catastrophic damage
to the helicopter and the passengers. The pilot learns to
identify hazards and how to deal with them when they are
incorporated into the training program.
Every flight has hazards and some level of risk associated
with it. It is critical that pilots be able to:
•
Differentiate, in advance, between a low-risk flight
and a high-risk flight.
•
Establish a review process and develop risk mitigation
strategies to address flights throughout that range.
Examining NTSB reports and other accident research can
help a pilot to assess risk more effectively. For example,
the accident rate decreases by nearly 50 percent once a
pilot obtains 100 hours, and continues to decrease until
the 1,000 hour level. The data suggest that for the first 500
hours, pilots flying visual flight rules (VFR) at night should
establish higher personal limitations than are required by the
regulations and, if applicable, apply instrument flying skills
in this environment.
Individuals training to be helicopter pilots should remember
that the helicopter accident rate is 30 percent higher than the
accident rate for fixed-wing aircraft. While many factors
contribute to this, students must recognize the small margin
of error that exists for helicopter pilots in making critical
decisions. In helicopters, certain emergency actions require
immediate action by the pilot. In the event of an engine
malfunction, failure to immediately lower the collective
results in rotor decay and failed autorotation. Fixed wing
pilots may have slightly more time to react and establish a
controllable descent. According to the General Aviation Joint
Steering Committee, the leading causes of accidents in GA
are CFIT, weather, runway incursions, pilot decision-making,
and loss of control. These causes are referred to as pilot-error,
or human factors related, accidents. CFIT, runway incursions,
and loss of control type accidents typically occur when the
pilot makes a series of bad judgments, which leads to these
events. For example, when the pilot has not adequately
planned the flight and the pilot subsequently fails to maintain
adequate situational awareness to avoid the terrain, a CFIT
accident occurs.
While the reasons for individual helicopter incidents vary,
it can be argued that it is the helicopter’s flight mode and
operational complexity that directly contributes to each
incident. By nature of its purpose, a helicopter usually flies
closer to terrain than does a fixed-wing aircraft. Subsequently,
minimal time exists to avoid CFIT, weather related, or loss
of control type incidents that require quick and accurate
assessments. Fixed-wing aircraft normally fly at higher
altitudes, and are flown from prepared surface to prepared
surface. Helicopters are often operated in smaller, confined
area-type environments and require continuous pilot control.
Helicopter pilots must be aware of what rotor wash can do
when landing to a dusty area or prior to starting where lose
debris may come in contact with the rotor blades.
Often, the loss of control occurs when the pilot exceeds
design or established operating standards, and the resulting
situation exceeds pilot capability to handle it successfully.
The FAA generally accepts these occurrences as resulting
from poor judgment. Likewise, most weather-related
accidents are not a result of the weather per se but of a failure
of the pilot to avoid a weather phenomenon for which the
aircraft is not equipped, or the pilot is not trained to handle.
That is, the pilot decides to fly or to continue into conditions
beyond pilot capability, commonly considered bad judgment.
It cannot be emphasized enough that the helicopter’s unique
capabilities come with increased risk. Since most helicopter
operations are conducted by a single pilot, the workload is
increased exponentially. Low-level maneuvering flight (a
catch-all category for different types of flying close to terrain
or obstacles, such as power line patrol, wildlife control, crop
dusting, air taxiing, and maneuvering for landing after an
instrument approach), is one of the largest single categories
of fatal accidents.
Fatal accidents that occur during approach often happen at
night or in instrument flight rules (IFR) conditions. Takeoff/
initial climb accidents are frequently due to the pilot’s lack
of awareness of the effects of density altitude on aircraft
performance or other improper takeoff planning that results
in loss of control during or shortly after takeoff. One of the
most lethal types of GA flying is attempting VFR flight into
instrument meteorological conditions (IMC). Accidents
involving poor weather decision-making account for about
4 percent of the total accidents but 14 percent of the fatal
mishaps. While weather forecast information has been
gradually improving, weather should remain a high priority
for every pilot assessing risk.
Using the 3P Model To Form Good Safety Habits
As discussed in the Pilot’s Handbook of Aeronautical
Knowledge, the Perceive, Process, Perform (3P) model helps
a pilot assess and manage risk effectively in the real world.
[Figure 14-6]
(Perceive)
Aeronautical
DecisionMaking
(Perform)
(Process)
Figure 14-6. 3P Model.
To use this model, the pilot will:
•
Perceive hazards
•
Process level of risk
• Perform risk management
Let’s put this to use through a common scenario, involving a
common task, such as a confined area approach. As is often
the case, the continuous loop consists of several elements;
each element must be addressed through the 3P process.
A utility helicopter pilot receives the task of flying four
passengers into a remote area for a hunting expedition. The
passengers have picked the location where they would like
to be dropped off based on the likelihood of wildlife patterns
for the area. The area has steep, rugged terrain in a series of
valleys and canyons leading up to large mountains.
Upon arrival at the location, the pilot locates a somewhat
large confined area near the base of one of the mountains.
The pilot begins the 3P process by quickly noting (or
perceiving) the hazards that affect the approach, landing,
and takeoff. Through thorough assessment the pilot takes
into consideration:
•
Current aircraft weight/power available,
•
Required approach angle to clear the trees for landing
in the confined area,
•
Wind direction and velocity,
•
Limited approach and departure paths (due to
constricting terrain),
14-11
•
Escape routes should the approach need to be
terminated prior to landing,
•
Possible hazards, such as wires or structures either
around the landing site or inside of the confined area,
and
•
The condition of the terrain at the landing site. Mud,
dust, and snow can be extreme hazards if the pilot
is not properly trained to land in those particular
conditions.
The pilot reviews the 3P process for each hazard. The pilot
has perceived the risk associated for each of the bullets listed
above. Now, the pilot assesses the risk level of each and what
to do to manage or mitigate the risk.
The aircraft weight/power risk is assessed as low. While
performing power checks, the pilot verified adequate out of
ground effect (OGE) power exists. The pilot is also aware
that, in this scenario, the departure DA (6,500 feet) is greater
than the arrival location DA (6,000 feet) and that several
hundred pounds of fuel have been burned off en route.
Furthermore, once the passengers have disembarked, more
power will be available for departure.
The pilot estimates that the highest obstacles along the
approach path are 70–80 feet in height. With the size of the
confined area, a normal approach angle can be maintained
to clear these obstacles, giving this a low risk level. To
further mitigate this risk the pilot has selected mental
checkpoints along the approach path that will serve as go/
no-go points should the pilot feel any assessed parameter is
being exceeded.
Wind direction and velocity are assessed as a medium risk
because (for this scenario) the direction of the wind is slightly
offset from the chosen approach path, creating a 15–20°
crosswind with a steady 10-knot wind. The pilot also takes
into consideration that, due to the terrain, the wind direction
and velocity may change during the approach. The pilot’s
experience and awareness of the complexity of mountain
flow wind provide a management tool for risk reduction.
From an approach and departure standpoint, the risk is
assessed to be medium. There is only one viable approach
and departure path. Given the size of the confined area and
the wind direction, the approach and departure path is deemed
acceptable.
The pilot assigns a medium risk level to the selection of an
escape route. The pilot is aware of the constricting terrain on
either side. Although adequate area exists for maneuvering,
the pilot realizes there are physical boundaries and that they
can affect the options available should the pilot need to
14-12
conduct a go-around or abort the approach. Again, the pilot
uses mental checkpoints to ensure an early decision is made
to conduct a go-around, if needed. The selected go-around
or escape route will be in line with the selected approach/
departure path and generally into the wind.
As you may have noticed, one identified hazard and its
correlating risk management action may have subsequent
impact on other factors. This demonstrates the need for
continuous assessment and evaluation of the impact of chosen
courses of action.
The 3P model offers three good reasons for its use. First, it
is fairly simple to remember. Second, it offers a structured,
efficient, and systematic way to identify hazards, assess risk,
and implement effective risk controls. Third, practicing risk
management needs to be as automatic as basic aircraft control.
As is true for other flying skills, risk management thinking
habits are best developed through repetition and consistent
adherence to specific procedures.
Once the pilot completes the 3P decision process and selects
a course of action, the process begins anew as the set of
circumstances brought about by the selected course of action
requires new analysis. Thus, the decision-making process is
a continuous loop of perceiving, processing, and performing.
Workload or Task Management
One component of SRM is workload or task management.
Research shows that humans have a limited capacity for
information. Once information flow exceeds the person’s
ability to mentally process the information, any additional
information becomes unattended or displaces other tasks
and information already being processed. Once this situation
occurs, only two alternatives exist: shed the unimportant
tasks or perform all tasks at a less than optimal level. Like
an overloaded electrical circuit, either the consumption must
be reduced or a circuit failure is experienced.
Effective workload management ensures essential operations
are accomplished by planning and then placing them in
a sequence that avoids work overload. As a pilot gains
experience, he or she learns to recognize future workload
requirements and can prepare for high workload periods
during times of low workload.
Reviewing the appropriate chart and setting radio frequencies
well in advance of need help reduce workload as a flight
nears the airport. In addition, a pilot should listen to
Automatic Terminal Information Service (ATIS), Automated
Surface Observing System (ASOS), or Automated Weather
Observing System (AWOS), if available, and then monitor
the tower frequency or Common Traffic Advisory Frequency
(CTAF) to get a good idea of what traffic conditions to
expect. Checklists should be performed well in advance so
there is time to focus on traffic and ATC instructions. These
procedures are especially important prior to entering a highdensity traffic area, such as Class B airspace.
To manage workload, items should be prioritized. For
example, during any situation, and especially in an
emergency, a pilot should remember the phrase “aviate,
navigate, and communicate.” This means that the first thing
a pilot should do is make sure the helicopter is under control,
then begin flying to an acceptable landing area. Only after the
first two items are assured should a pilot try to communicate
with anyone.
Another important part of managing workload is recognizing
a work overload situation. The first effect of high workload
is that a pilot begins to work faster. As workload increases,
attention cannot be devoted to several tasks at one time, and
a pilot may begin to focus on one item. When a pilot becomes
task saturated, there is no awareness of additional inputs from
various sources, so decisions may be made on incomplete
information, and the possibility of error increases.
A very good example of this is inadvertent IMC. Once
entering into bad weather, work overload becomes
immediate. Mentally, the pilot must transition from flying
outside of the aircraft to flying inside the aircraft. Losing
all visual references can cause sensory overload and the
ability to think rationally is gone. Instead of trusting the
aircrafts instruments, pilots try to hang on to the little visual
references that they have and forget all about the other factors
surrounding them. Instead of slowing the helicopter down
they increase airspeed. Because they are looking down for
visual references they forget about the hazards in front of
them and finally, because they are not looking at the flight
instruments, the aircraft is not level. All of this can be avoided
by proper training and proper planning. If going inadvertent
IMC is your only course of action, pilots must commit to it
and fly the helicopter using only the flight instruments and
not trying to follow what little visual references they have.
When a work overload situation exists, a pilot needs to:
•
Stop,
•
Think,
•
Slow down, and then
•
Prioritize.
It is important for a pilot to understand how to decrease
workload by:
•
Placing a situation in the proper perspective,
•
Remaining calm, and
•
Thinking rationally.
These key elements reduce stress and increase the pilot’s
ability to fly safely. They depend upon the experience,
discipline, and training that each safe flight earns. It is
important to understand options available to decrease
workload. For example, setting a radio frequency may be
delegated to another pilot or passenger, freeing the pilot to
perform higher priority tasks.
Situational Awareness
In addition to learning to make good aeronautical decisions,
and learning to manage risk and flight workload, situation
awareness (SA) is an important element of ADM. Situational
awareness is the accurate perception and understanding of
all the factors and conditions within the four fundamental
risk elements (PAVE) that affect safety before, during, and
after the flight. Situation awareness (SA) involves being
aware of what is happening around you to understand how
information, events, and your own actions will impact your
goals and objectives, both now and in the near future. Lacking
SA or having inadequate SA has been identified as one of
the primary factors in accidents attributed to human error
Situational awareness in a helicopter can be quickly lost.
Understanding the significance and impact of each risk factor
independently and cumulatively aid in safe flight operations.
It is possible, and all too likely, that we forget flying while
at work. Our occupation, or work, may be conducting long
line operations, maneuvering around city obstacles to allow
a film crew access to news events, spraying crops, ferrying
passengers or picking up a patient to be flown to a hospital.
In each case we are flying a helicopter. The moment we
fail to account for the aircraft systems, the environment,
other aircraft, hazards, and ourselves, we lose situational
awareness.
To maintain SA, all of the skills involved in SRM are
used. For example, an accurate perception of pilot fitness
can be achieved through self-assessment and recognition
of hazardous attitudes. A clear assessment of the status of
navigation equipment can be obtained through workload
management, while establishing a productive relationship
with ATC can be accomplished by effective resource use.
14-13
Obstacles to Maintaining Situational Awareness
What distractions interfere with our focus or train of thought?
There are many. A few examples pertinent to aviation, and
helicopters specifically, follow.
Fatigue, frequently associated with pilot error, is a threat to
aviation safety because it impairs alertness and performance.
[Figure 14-7] The term is used to describe a range of
experiences from sleepy or tired to exhausted. Two major
physiological phenomena create fatigue: circadian rhythm
disruption and sleep loss.
Many helicopter jobs require scheduling flexibility,
frequently affecting the body’s circadian rhythm. You may
be flying a day flight Monday and then at night on Tuesday.
Your awareness of how your body and mind react to this
variation in schedule is vital to safety. This disruptive pattern
may result in degradation of attention and concentration,
impaired coordination, and decreased ability to communicate.
Physical fatigue results from sleep loss, exercise, or physical
work. Factors such as stress and prolonged performance of
cognitive work result in mental fatigue. Consecutive days
of flying the maximum allowable flight time can fatigue a
pilot, mentally and physically. It is important to take breaks
within the workday, as well as days off when possible.
When you find yourself in this situation, take an objective,
honest assessment of your state of mind. If necessary, use
rest periods to allow rejuvenation of the mind and body.
[Figure 14-8]
Fatigue also occurs under circumstances in which there is
anticipation of flight followed by inactivity. For instance,
a pilot is given a task requiring a specific takeoff time. In
anticipation of the flight, the pilot’s adrenaline kicks in and
situational awareness is elevated. After a delay (weather,
Countermeasures
Long naps (3–4 hours*) can restore alertness
for 12–15 hours.
Short power naps (10–30 minutes*)
can restore alertness for 3–4 hours.
Eat high-protein meals.
Drink plenty of fluids, especially water.
Rotate flight tasks and converse with other
crew members or passengers.
Keep the flight deck temperature cool.
Move/stretch in the seat, and periodically
get up to walk around the aircraft, if possible.
* Allow 15–20 minutes after awakening to become fully
alert before assuming aircrew duties.
Figure 14-8. Countermeasures to fatigue according to the FAA
Civil Aerospace Medical Institute (CAMI).
maintenance, or any other unforeseen delay), the pilot feels a
let down, in effect, becoming fatigued. Then, upon resuming
the flight, the pilot does not have that same level of attention.
Complacency presents another obstacle to maintaining
situational awareness. Defined as overconfidence from
repeated experience with a specific activity, complacency
has been implicated as a contributing factor in numerous
aviation accidents and incidents. When activities become
routine, a pilot may have a tendency to relax and not put as
much effort into performance. Like fatigue, complacency
reduces a pilot’s effectiveness on the flight deck. However,
complacency is more difficult to recognize than fatigue, since
everything seems to be progressing smoothly.
z
z
z
Spotty short-term memory
Wandering or poorly organized thoughts
Missed or erroneous performance of routine procedures
Degradation of control accuracy
Figure 14-7. Warning signs of fatigue according to the FAA Civil Aerospace Medical Institute (CAMI).
14-14
50
30
Vision going in and out of focus
Persistent yawning
70
60
40
Warning Signs of Fatigue
Head bobbing involuntarily
90
80
Since complacency seems to creep into our routine without
notice, ask what has changed. The minor changes that go
unnoticed can be associated with the four fundamental risks
we previously discussed: pilot, aircraft, environment, and
external pressures.
As a pilot, am I still using checklists or have I become reliant
on memory to complete my checks? Do I check NOTAMs
before every flight or only when I think it is necessary? And
the aircraft: did I feel that vibration before or is it new? Was
there a log book entry for it? If so, has it been checked?
Complacent acceptance of common weather patterns can
have huge impacts on safety. The forecast was for clearing
after the rain shower, but what was the dew-point spread?
The winds are greater than forecast. Will this create reduced
visibility in dusty, snowy areas or exceed wind limitations?
While conducting crop spraying, a new agent is used.
Does that change the weight? Does that change the flight
profile and, if so, what new hazards might be encountered?
When things are going smoothly, it is time to heighten your
awareness and become more attentive to your flight activities.
Advanced avionics have created a high degree of redundancy
and dependability in modern aircraft systems, which can
promote complacency and inattention. Routine flight
operations may lead to a sense of complacency, which can
threaten flight safety by reducing situational awareness.
Loss of situational awareness can be caused by a minor
distraction that diverts the pilot’s attention from monitoring
the instruments or scanning outside the aircraft. For example,
a gauge that is not reading correctly is a minor problem,
but it can cause an accident if the pilot diverts attention to
the perceived problem and neglects to control the aircraft
properly.
Operational Pitfalls
There are numerous classic behavioral traps that can
ensnare the unwary pilot. Pilots, particularly those with
considerable experience, try to complete a flight as planned,
please passengers, and meet schedules. This basic drive to
achieve can have an adverse effect on safety and can impose
an unrealistic assessment of piloting skills under stressful
conditions. These tendencies ultimately may bring about
practices that are dangerous and sometimes illegal, and may
lead to a mishap. Pilots develop awareness and learn to avoid
many of these operational pitfalls through effective SRM
training. [Figure 14-9]
Controlled Flight Into Terrain (CFIT)
Awareness
An emergency medical services (EMS) helicopter departed
for a night flight to transport an 11-day-old infant patient
from one hospital to another. No record was found indicating
the pilot obtained a weather briefing before departure. The
pilot had a choice of taking either a direct route that crossed
a remote area of rugged mountainous terrain with maximum
ground elevations of about 9,000 feet or a route that was about
10 minutes longer and followed an interstate highway with
maximum ground elevations of about 6,000 feet. Radar data,
which show about 4 minutes of the helicopter’s flight before
coverage was lost due to mountainous terrain, are consistent
with the flight following the direct route.
A search was initiated about 4 hours after the helicopter did
not arrive at the destination hospital, and the wreckage was
located the following morning. Physical evidence observed
at the accident site indicated that the helicopter was in level
flight at impact and was consistent with CFIT. [Figure 14-10]
CFIT is a type of accident that continues to be a major safety
concern, while at the same time difficult to explain because
it involves a pilot controlling an airworthy aircraft that is
flown into terrain (water or obstacles) with inadequate pilot
awareness of the impending disaster.
One constant in CFIT accidents is that outside visibility is
limited, or the accident occurs at night and the terrain is not
seen easily until just prior to impact. Another commonality
among CFIT accidents is lack of situational awareness. This
includes not only horizontal awareness, knowing where the
helicopter is over the ground, but also vertical awareness.
Training, planning, and preparation are a pilot’s best defenses
for avoiding CFIT accidents. For example, take some time
before takeoff to become familiar with the proposed flight and
the terrain. Avoidance of CFIT begins before the helicopter
departs the home location. Proper planning, including applied
risk mitigation must occur before the aircraft is even started.
Thorough assessment of terrain, visibility, pilot experience
and available contingencies must be conducted. If necessary,
delay or postpone the flight while on the ground. The decision
to abort the flight is much easier to make in the planning room
than in the air. In case conditions deteriorate once in flight.
Have contingency options available.
While many CFIT accidents and incidents occur during
nonprecision approaches and landings, great measures have
14-15
Operational Pitfalls
Peer Pressure
It would be foolish and unsafe for a new pilot to attempt to compete with an older, more experienced pilot. The only safe competition
should be completing the most safe flights with no one endangered or hurt and the aircraft returned to service. Efficiency comes with
experience and on-the-job training.
Mind Set
A pilot should be taught to approach every day as something new.
Get-There-Itis
This disposition impairs pilot judgment through a fixation on the original goal or destination, combined with a disregard for any
alternative course of action.
Duck-Under Syndrome
A pilot may be tempted to arrive at an airport by descending below minimums during an approach. There may be a belief that
there is a built-in margin of error in every approach procedure, or the pilot may not want to admit that the landing cannot be
completed and a missed approach must be initiated.
Scud Running
It is difficult for a pilot to estimate the distance from indistinct forms, such as clouds or fog formation.
Continuing Visual Flight Rules (VFR) Into Instrument Conditions
Spatial disorientation or collision with ground/obstacles may occur when a pilot continues VFR into instrument conditions. This can
be even more dangerous if the pilot is not instrument rated or current.
Getting Behind the Aircraft
This pitfall can be caused by allowing events or the situation to control pilot actions. A constant state of surprise at what happens
next may be exhibited when the pilot is “getting behind” the aircraft.
Loss of Positional or Situational Awareness
In extreme cases of a pilot getting behind the aircraft, a loss of positional or situational awareness may result. The pilot may not
know the aircraft’s geographical location, or may be unable to recognize deteriorating circumstances.
Operating Without Adequate Fuel Reserves
Pilots should use the last of the known fuel to make a safe landing. Bringing fuel to an aircraft is much less inconvenient than
picking up the pieces of a crashed helicopter! Pilots should land prior to whenever their watch, fuel gauge, low-fuel warning system,
or flight planning indicates fuel burnout. They should always be thinking of unforecast winds, richer-than-planned mixtures,
unknown leaks, mis-servicing, and errors in planning. Newer pilots need to be wary of fuselage attitudes in low-fuel situations.
Some helicopters can port air into the fuel system in low-fuel states, causing the engines to quit or surge.
Descent Below the Minimum En Route Altitude
The duck-under syndrome, as mentioned above, can also occur during the en route portion of an IFR flight.
Flying Outside the Envelope
The pilot must understand how to check the charts, understand the results, and fly accordingly.
Neglect of Flight Planning, Preflight Inspections, and Checklists
All pilots and operators must understand the complexity of the helicopter, the amazing number of parts, and why there are service
times associated with certain parts. Pilots should understand material fatigue and maintenance requirements. Helicopters are
unforgiving of disregarded maintenance requirements. Inspections and maintenance are in place for safety; something functioning
improperly can be the first link in the error chain to an accident. In some cases, proper maintenance is a necessary condition for
insurance converage.
Figure 14-9. Operational pitfalls.
been taken to improve instrument training, equipment and
procedures. For the qualified pilot, instrument flight should
not be avoided, but rather, trained as a viable option for safely
recovering the aircraft. Like any other training, frequent
instrument training builds confidence and reassurance.
14-16
Good instrument procedures include studying approach
charts before leaving cruise altitude. Key fixes and airport
elevation must be noted and associated with terrain and
obstacles along the approach path. Pilots should have a good
understanding of both approach and departure design criteria
therefore, hover height should be increased to avoid contact
with obstacles and hover speed should be reduced. Weather
conditions can be very deceptive and difficult to detect in
flight under night conditions. On a low-illumination night,
it is easy to fly into clouds without realizing it before it is
too late to correct.
Due to the number of recent CFIT night accidents, the NTSB
issued a safety alert in 2008 about avoiding night CFIT
accidents. That alert included the following information:
•
Terrain familiarization is critical to safe visual
operations at night. Use sectional charts or other
topographic references to ensure the helicopter will
safely clear terrain and obstructions all along the route.
•
When planning a nighttime VFR flight, follow IFR
practices, such as climbing on a known safe course
until well above surrounding terrain. Choose a cruising
altitude that provides terrain separation similar to IFR
flights (2,000 feet above ground level in mountainous
areas and 1,000 feet above the ground in other areas).
Using this technique, known obstacles, such as towers,
will be avoided.
•
When receiving radar services, do not depend on ATC
to warn of terrain hazards. Although controllers try
to warn pilots if they notice a hazardous situation,
they may not always recognize that a particular VFR
aircraft is dangerously close to terrain.
•
When ATC issues a heading with an instruction to
“maintain VFR,” be aware that the heading may
not provide adequate terrain clearance. If any doubt
exists about your ability to avoid terrain and obstacles
visually, advise ATC immediately and take action to
reach a safe altitude.
•
For improved night vision, the FAA recommends the
use of supplemental oxygen for flights above 5,000
feet.
•
Obtain as much information about areas in which you
will be flying and the routes to by utilizing hazard
maps and satellite imagery.
•
Before flying at night to unfamiliar remote areas or
areas with hazardous terrain, try to arrange a day flight
for familiarization.
•
If a pilot flies at night, especially in remote or unlit
areas, consider whether a global positioning system
(GPS)-based terrain awareness unit would improve
the safety of the flight.
Figure 14-10. Helicopter heading straight for mountain.
to understand fully the obstacle clearance margins built into
them. Some pilots have the false belief that ATC provides
obstacle clearance while en route off airways. The pilot is
ultimately responsible for obstacle clearance.
Altitude error is another common cause of CFIT. Cases
of altitude error involve disorientation with respect to the
NAVAID, improper transition on approach, selecting the
wrong NAVAID, or just plain lack of horizontal situational
awareness. Today’s modern aircraft have sophisticated flight
directors, autopilots, autothrottles, and flight management
systems. These devices make significant contributions to
the overall safety of flight, but they are only machines that
follow instructions. They do whatever is asked of them, even
if it is wrong. When commanded, they unerringly follow
instructions—sometimes straight into the ground. The pilot
must ensure that both vertical and horizontal modes are
correct and engaged. Cross-check autopilots constantly.
When automated flight equipment is not available, great care
must be taken to prepare properly for a night flight. SRM
becomes more challenging under the cover of darkness and
caution should be exercised when determining what artificial
light source to use inside the aircraft. A light source that is
too bright will blind the pilot from seeing outside obstacles
or rising terrain. Certain colored lenses bleach out symbols
and markings on a map. Conduct this planning on the ground,
in a dark room if necessary, before the actual flight.
Pilots must be even more conservative with their decisionmaking and planning when flying at night. Flying becomes
more difficult due to the degradation of our sensory perception
and the lack of outside references. Beginning with preflight,
looking over the helicopter with a flashlight can cause pilots
to miss even the smallest discrepancy that they would easily
see during the day. For example, failing to remove one or all
if the tie downs and attempting to take off would probably
result in a dynamic rollover accident. Whenever possible,
preflight inspection should always be conducted during the
day or in a lighted hangar. Depth perception is less acute;
Of particular note in the 2008 safety alert is a comment
regarding oxygen use above 5,000 feet. Most helicopters
are neither required nor equipped for supplemental oxygen
use at this altitude. Due to the physiological importance
14-17
of oxygen in night vision, care should be taken to exercise
light discipline. Interior lighting should be lowered to the
lowest possible levels, but must allow adequate illumination
of necessary systems and instruments. This, in turn, allows
greater recognition of outside obstacles and terrain features.
Limited outside visibility is one constant in CFIT accidents.
In the accident cited at the beginning of this section, it appears
the pilot failed to obtain a weather briefing. If the pilot had
obtained one, he would probably have learned of the cloud
cover and light precipitation present along his planned route
of flight. The limited outside visibility probably caused the
CFIT accident since no evidence was found of any pre-impact
mechanical discrepancies with the helicopter’s airframe or
systems that would have prevented normal operation.
Automation Management
Automation management is the control and navigation of an
aircraft by means of the automated systems installed in the
aircraft. One of the most important concepts of automation
management is simply knowing when to use it and when
not to use it.
Ideally, a pilot first learns to perform practical test standard
(PTS) maneuvers and procedures in the aircraft manually,
or hand flying. After successfully demonstrating proficiency
in the basic maneuvers, the pilot is then introduced to the
available automation and/or the autopilot. Obviously, in some
aircraft, not all automated systems may be disengaged for
basic flight. The purpose of basic flight without automation is
to ensure the pilot can hand fly the maneuver when necessary.
Advanced avionics offer multiple levels of automation, from
strictly manual flight to highly automated flight. No one level
of automation is appropriate for all flight situations, but to
avoid potentially dangerous distractions when flying with
advanced avionics, the pilot must know how to manage the
course indicator, the navigation source, and the autopilot.
It is important for a pilot to know the peculiarities of the
particular automated system in use. This ensures the pilot
knows what to expect, how to monitor for proper operation,
and promptly take appropriate action if the system does not
perform as expected.
14-18
At the most basic level, managing the autopilot means
knowing at all times which modes are engaged and which
modes are armed to engage. The pilot needs to verify that
armed functions (e.g., navigation tracking or altitude capture)
engage at the appropriate time. Automation management is a
good place to practice the call-out technique, especially after
arming the system to make a change in course or altitude.
Chapter Summary
This chapter focused on aeronautical decision-making, which
includes SRM training, risk management, workload or task
management, situational awareness, CFIT awareness, and
automation management. Factors affecting a helicopter
pilot’s ability to make safe aeronautical decisions were also
discussed. The importance of learning how to be aware of
potential risks in flying, how to clearly identify those risks,
and how to manage them successfully were also explored.
Glossary
Absolute altitude. The actual distance an object is above
the ground.
Advancing blade. The blade moving in the same direction as
the helicopter. In helicopters that have counterclockwise main
rotor blade rotation as viewed from above, the advancing
blade is in the right half of the rotor disk area during forward
movement.
Agonic Line. An isogonic line along which there is no
magnetic variation.
Air density. The density of the air in terms of mass per unit
volume. Dense air has more molecules per unit volume than
less dense air. The density of air decreases with altitude above
the surface of the earth and with increasing temperature.
Aircraft pitch. The movement of the aircraft about its lateral,
or pitch, axis. Movement of the cyclic forward or aft causes
the nose of the helicopter to pitch up or down.
Antitorque rotor. See tail rotor.
Articulated rotor. A rotor system in which each of the blades
is connected to the rotor hub in such a way that it is free to
change its pitch angle, and move up and down and fore and
aft in its plane of rotation.
Autopilot. Those units and components that furnish a means
of automatically controlling the aircraft.
Autorotation. The condition of flight during which the main
rotor is driven only by aerodynamic forces with no power
from the engine.
Axis of rotation. The imaginary line about which the rotor
rotates. It is represented by a line drawn through the center
of, and perpendicular to, the tip-path plane.
Basic empty weight. The weight of the standard helicopter,
operational equipment, unusable fuel, and full operating
fluids, including full engine oil.
Aircraft roll. The movement of the aircraft about its
longitudinal axis. Movement of the cyclic right or left causes
the helicopter to tilt in that direction.
Blade coning. An upward sweep of rotor blades as a result
of lift and centrifugal force.
Airfoil. Any surface designed to obtain a useful reaction of
lift, or negative lift, as it moves through the air.
Blade damper. A device attached to the drag hinge to restrain
the fore and aft movement of the rotor blade.
Airworthiness Directive. When an unsafe condition exists
with an aircraft, the FAA issues an Airworthiness Directive
to notify concerned parties of the condition and to describe
the appropriate corrective action.
Blade feather or feathering. The rotation of the blade around
the spanwise (pitch change) axis.
Altimeter. An instrument that indicates flight altitude by
sensing pressure changes and displaying altitude in feet or
meters.
Angle of attack. The angle between the airfoil’s chord line
and the relative wind.
Blade flap. The ability of the rotor blade to move in a vertical
direction. Blades may flap independently or in unison.
Blade grip. The part of the hub assembly to which the rotor
blades are attached, sometimes referred to as blade forks.
Blade lead or lag. The fore and aft movement of the blade
in the plane of rotation. It is sometimes called “hunting” or
“dragging.”
Antitorque pedal. The pedal used to control the pitch of the
tail rotor or air diffuser in a NOTAR® system.
G-1
Blade loading. The load imposed on rotor blades, determined
by dividing the total weight of the helicopter by the combined
area of all the rotor blades.
Blade root. The part of the blade that attaches to the blade
grip.
warning lights located on the instrument panel that illuminate
when metal particles are picked up.
Chord. An imaginary straight line between the leading and
trailing edges of an airfoil section.
Blade span. The length of a blade from its tip to its root.
Chordwise axis. For semirigid rotors, a term used to describe
the flapping or teetering axis of the rotor.
Blade stall. The condition of the rotor blade when it is
operating at an angle of attack greater than the maximum
angle of lift.
Coaxial rotor. A rotor system utilizing two rotors turning
in opposite directions on the same centerline. This system is
used to eliminated the need for a tail rotor.
Blade tip. The furthermost part of the blade from the hub
of the rotor.
Collective pitch control. The control for changing the pitch
of all the rotor blades in the main rotor system equally and
simultaneously and, consequently, the amount of lift or thrust
being generated.
Blade track. The relationship of the blade tips in the plane
of rotation. Blades that are in track will move through the
same plane of rotation.
Blade tracking. The mechanical procedure used to bring the
blades of the rotor into a satisfactory relationship with each
other under dynamic conditions so that all blades rotate on
a common plane.
Blade twist. The variation in the angle of incidence of a blade
between the root and the tip.
Blowback. The tendency of the rotor disk to tilt aft in
transition to forward flight as a result of unequal airflow.
Calibrated airspeed (CAS). Indicated airspeed of an aircraft,
corrected for installation and instrumentation errors.
Coning. See blade coning.
Coriolis effect. The tendency of a rotor blade to increase or
decrease its velocity in its plane of rotation when the center
of mass moves closer to or farther from the axis of rotation.
Cyclic feathering. The mechanical change of the angle of
incidence, or pitch, of individual rotor blades, independent
of other blades in the system.
Cyclic pitch control. The control for changing the pitch of
each rotor blade individually as it rotates through one cycle
to govern the tilt of the rotor disk and, consequently, the
direction and velocity of horizontal movement.
Center of gravity. The theoretical point where the entire
weight of the helicopter is considered to be concentrated.
Delta hinge. A flapping hinge with an axis skewed so that
the flapping motion introduces a component of feathering that
would result in a restoring force in the flap-wise direction.
Center of pressure. The point where the resultant of all the
aerodynamic forces acting on an airfoil intersects the chord.
Density altitude. Pressure altitude corrected for nonstandard
temperature variations.
Centrifugal force. The apparent force that an object moving
along a circular path exerts on the body constraining the
object and that acts outwardly away from the center of
rotation.
Deviation. A compass error caused by magnetic disturbances
from the electrical and metal components in the aircraft. The
correction for this error is displayed on a compass correction
card placed near the magnetic compass of the aircraft.
Centripetal force. The force that attracts a body toward its
axis of rotation. It is opposite centrifugal force.
Direct control. The ability to maneuver a helicopter by tilting
the rotor disk and changing the pitch of the rotor blades.
Chip detector. A warning device that alerts you to any
abnormal wear in a transmission or engine. It consists of a
magnetic plug located within the transmission. The magnet
attracts any metal particles that have come loose from the
bearings or other transmission parts. Most chip detectors have
Direct shaft turbine. A single-shaft turbine engine in which
the compressor and power section are mounted on a common
driveshaft.
G-2
Disk area. The area swept by the blades of the rotor. It is
a circle with its center at the hub and has a radius of one
blade length.
Disk loading. The total helicopter weight divided by the
rotor disk area.
Dissymmetry of lift. The unequal lift across the rotor disk
resulting from the difference in the velocity of air over the
advancing blade half and the velocity of air over the retreating
blade half of the rotor disk area.
Drag. An aerodynamic force on a body acting parallel and
opposite to relative wind.
Gravity. See weight.
Gross weight. The sum of the basic empty weight and
useful load.
Ground effect. A usually beneficial influence on helicopter
performance that occurs while flying close to the ground. It
results from a reduction in upwash, downwash, and bladetip
vortices, which provide a corresponding decrease in induced
drag.
Ground resonance. Selfexcited vibration occurring
whenever the frequency of oscillation of the blades about the
lead-lag axis of an articulated rotor becomes the same as the
natural frequency of the fuselage.
Dual rotor. A rotor system utilizing two main rotors.
Dynamic rollover. The tendency of a helicopter to continue
rolling when the critical angle is exceeded, if one gear is on
the ground, and the helicopter is pivoting around that point.
Feathering. The action that changes the pitch angle of
the rotor blades by rotating them around their feathering
(spanwise) axis.
Feathering axis. The axis about which the pitch angle of a
rotor blade is varied. Sometimes referred to as the spanwise
axis.
Feedback. The transmittal of forces, which are initiated by
aerodynamic action on rotor blades, to the cockpit controls.
Flapping. The vertical movement of a blade about a flapping
hinge.
Flapping hinge. The hinge that permits the rotor blade to
flap and thus balance the lift generated by the advancing and
retreating blades.
Flare. A maneuver accomplished prior to landing to slow
a helicopter.
Free turbine. A turboshaft engine with no physical
connection between the compressor and power output shaft.
Freewheeling unit. A component of the transmission or
power train that automatically disconnects the main rotor
from the engine when the engine stops or slows below the
equivalent rotor rpm.
Fully articulated rotor system. See articulated rotor system.
Gyroscopic procession. An inherent quality of rotating
bodies, which causes an applied force to be manifested 90°
in the direction of rotation from the point where the force
is applied.
Human factors. The study of how people interact with their
environment. In the case of general aviation, it is the study
of how pilot performance is influenced by such issues as the
design of cockpits, the function of the organs of the body, the
effects of emotions, and the interaction and communication
with other participants in the aviation community, such as
other crew members and air traffic control personnel.
Hunting. Movement of a blade with respect to the other
blades in the plane of rotation, sometimes called leading or
lagging.
In ground effect (IGE) hover. Hovering close to the surface
(usually less than one rotor diameter distance above the
surface) under the influence of ground effect.
Induced drag. That part of the total drag that is created by
the production of lift.
Induced flow. The component of air flowing vertically
through the rotor system resulting from the production of lift.
Inertia. The property of matter by which it will remain at rest
or in a state of uniform motion in the same direction unless
acted upon by some external force.
Isogonic line. Lines on charts that connect points of equal
magnetic variation.
Knot. A unit of speed equal to one nautical mile per hour.
G-3
LDMAX. The maximum ratio between total lift (L) and total
drag (D). This point provides the best glide speed. Any
deviation from the best glide speed increases drag and reduces
the distance you can glide.
Lateral vibration. A vibration in which the movement is
in a lateral direction, such as imbalance of the main rotor.
Lead and flag. The fore (lead) and aft (lag) movement of
the rotor blade in the plane of rotation.
Licensed empty weight. Basic empty weight not including
full engine oil, just undrainable oil.
Lift. One of the four main forces acting on a helicopter. It
acts perpendicular to the relative wind.
Load factor. The ratio of a specified load weight to the total
weight of the aircraft.
Married needles. A term used when two hands of an
instrument are superimposed over each other, as on the
engine/rotor tachometer.
Mast. The component that supports the main rotor.
Mast bumping. Action of the rotor head striking the mast,
occurring on underslung rotors only.
Navigational aid (NAVAID). Any visual or electronic
device, airborne or on the surface, that provides point-to-point
guidance information, or position data, to aircraft in flight.
Night. The time between the end of evening civil twilight
and the beginning of morning civil twilight, as published in
the American Air Almanac.
Normally aspirated engine. An engine that does not
compensate for decreases in atmospheric pressure through
turbocharging or other means.
One-to-one vibration. A low frequency vibration having
one beat per revolution of the rotor. This vibration can be
either lateral, vertical, or horizontal.
Out of ground effect (OGE) hover. Hovering a distance
greater than one disk diameter above the surface. Because
induced drag is greater while hovering out of ground effect,
it takes more power to achieve a hover out of ground effect.
Parasite drag. The part of total drag created by the form or
shape of helicopter parts.
G-4
Payload. The term used for the combined weight of
passengers, baggage, and cargo.
Pendular action. The lateral or longitudinal oscillation of
the fuselage due to its suspension from the rotor system.
Pitch angle. The angle between the chord line of the rotor
blade and the reference plane of the main rotor hub or the
rotor plane of rotation.
Pressure altitude. The height above the standard pressure
level of 29.92 "Hg. It is obtained by setting 29.92 in the
barometric pressure window and reading the altimeter.
Profile drag. Drag incurred from frictional or parasitic
resistance of the blades passing through the air. It does not
change significantly with the angle of attack of the airfoil
section, but it increases moderately as airspeed increases.
Resultant relative wind. Airflow from rotation that is
modified by induced flow.
Retreating blade. Any blade, located in a semicircular part
of the rotor disk, in which the blade direction is opposite to
the direction of flight.
Retreating blade stall. A stall that begins at or near the tip
of a blade in a helicopter because of the high angles of attack
required to compensate for dissymmetry of lift.
Rigid rotor. A rotor system permitting blades to feather,
but not flap or hunt.
Rotational velocity. The component of relative wind
produced by the rotation of the rotor blades.
Rotor. A complete system of rotating airfoils creating lift
for a helicopter.
Rotor brake. A device used to stop the rotor blades during
shutdown.
Rotor disk area. See disk area.
Rotor force. The force produced by the rotor, comprised of
rotor lift and rotor drag.
Semirigid rotor. A rotor system in which the blades are fixed
to the hub, but are free to flap and feather.
Settling with power. See vortex ring state.
Shaft turbine. A turbine engine used to drive an output shaft,
commonly used in helicopters.
Skid. A flight condition in which the rate of turn is too great
for the angle of bank.
Skid shoes. Plates attached to the bottom of skid landing
gear, protecting the skid.
Slip. A flight condition in which the rate of turn is too slow
for the angle of bank.
Solidity ratio. The ratio of the total rotor blade area to total
rotor disk area.
Span. The dimension of a rotor blade or airfoil from root
to tip.
Split needles. A term used to describe the position of the
two needles on the engine/rotor tachometer when the two
needles are not superimposed.
Torque. In helicopters with a single, main rotor system, the
tendency of the helicopter to turn in the opposite direction
of the main rotor rotation.
Trailing edge. The rearmost edge of an airfoil.
Translating tendency. The tendency of the single-rotor
helicopter to move laterally during hovering flight. Also
called tail rotor drift.
Translational lift. The additional lift obtained when entering
forward flight, due to the increased efficiency of the rotor
system.
Transverse-flow effect. The condition of increased drag
and decreased lift in the aft portion of the rotor disk caused
by the air having a greater induced velocity and angle in the
aft portion of the disk.
True altitude. The actual height of an object above mean
sea level.
Standard atmosphere. A hypothetical atmosphere based on
averages in which the surface temperature is 59 °F (15 °C),
the surface pressure is 29.92 "Hg (1013.2 Mb) at sea level,
and the temperature lapse rate is approximately 3.5 °F (2
°C) per 1,000 feet.
Turboshaft engine. A turbine engine transmitting power
through a shaft as would be found in a turbine helicopter.
Static stop. A device used to limit the blade flap, or rotor
flap, at low rpm or when the rotor is stopped.
Underslung. A rotor hub that rotates below the top of the
mast, as on semirigid rotor systems.
Steady-state flight. The type of flight experienced when a
helicopter is in straight-and-level, unaccelerated flight, and
all forces are in balance.
Unloaded rotor. The state of a rotor when rotor force has
been removed, or when the rotor is operating under a low or
negative G condition.
Symmetrical airfoil. An airfoil having the same shape on
the top and bottom.
Useful load. The difference between the gross weight and
the basic empty weight. It includes the flight crew, usable
fuel, drainable oil, if applicable, and payload.
Tail rotor. A rotor turning in a plane perpendicular to that
of the main rotor and parallel to the longitudinal axis of the
fuselage. It is used to control the torque of the main rotor and
to provide movement about the yaw axis of the helicopter.
Teetering hinge. A hinge that permits the rotor blades of a
semirigid rotor system to flap as a unit.
Thrust. The force developed by the rotor blades acting
parallel to the relative wind and opposing the forces of drag
and weight.
Tip-path plane. The imaginary circular plane outlined by
the rotor blade tips as they make a cycle of rotation.
Twist grip. The power control on the end of the collective
control.
Variation. The angular difference between true north and
magnetic north; indicated on charts by isogonic lines.
Vertical vibration. A vibration in which the movement is
up and down, or vertical, as in an out-of-track condition.
Vortex ring state. A transient condition of downward flight
(descending through air after just previously being accelerated
downward by the rotor) during which an appreciable portion
of the main rotor system is being forced to operate at angles
of attack above maximum. Blade stall starts near the hub and
progresses outward as the rate of descent increases.
G-5
Weight. One of the four main forces acting on a helicopter.
Equivalent to the actual weight of the helicopter. It acts
downward toward the center of the earth.
Yaw. The movement of a helicopter about its vertical axis.
G-6
Index
A
C
Abnormal vibrations...................................................11-21
Accessory gearbox........................................................4-10
Advancing blade...........................................................2-18
Aeronautical decision-making (ADM).........................14-2
After landing and securing..............................................8-6
Aircraft servicing............................................................8-3
Airflow............................................................................2-8
horizontal part.............................................................2-8
in forward flight.........................................................2-17
vertical part..................................................................2-8
Airfoil..............................................................................2-6
nonsymmetrical airfoil (cambered).............................2-7
symmetrical airfoil......................................................2-7
Airframe..........................................................................4-1
Altimeter.......................................................................12-2
Angle of attack (AOA).......................................... 2-7, 2-10
Angle of incidence................................................ 2-7, 2-10
Anti-icing systems........................................................4-18
Antitorque drive systems................................................4-8
antitorque pedals..................................................... 1-6, 3-4
Antitorque system...........................................................4-7
Fenestron.....................................................................4-7
NOTAR®....................................................................4-7
Antitorque system failure............................................11-16
AOA................................................................................2-7
Approach and landing....................................... 10-11, 13-9
Approaches...................................................................9-19
Astigmatism..................................................................13-2
Atmospheric illusions...................................................13-9
Autopilot.......................................................................4-17
Autorotation..................................................................2-24
Autorotation (forward flight)........................................2-25
Autorotation with turns.................................................11-5
Carburetor ice................................................................4-13
Center of gravity.............................................................6-2
Center of pressure...........................................................2-7
Centrifugal clutch..........................................................4-11
CG aft of aft limit............................................................6-3
Chord..............................................................................2-6
Chord line........................................................................2-6
Clutch............................................................................4-11
Coaxial rotors..................................................................1-3
Cockpit lights................................................................13-8
Collective........................................................................1-5
Collective pitch control........................................... 1-5, 3-2
Collision avoidance at night..........................................13-9
Combustion chamber......................................................4-9
Common errors of attitude instrument flying................12-4
emphasis....................................................................12-4
omission....................................................................12-4
Compressor.....................................................................4-8
Coning...........................................................................2-14
Control inputs.................................................................1-5
antitorque pedals.........................................................1-5
collective.....................................................................1-5
cyclic...........................................................................1-5
throttle.........................................................................1-5
Coriolis Effect (Law of Conservation of Angular
Momentum)...................................................................2-15
Critical conditions.......................................................11-12
Crosswind considerations during takeoffs....................9-10
B
Basic empty weight.........................................................6-2
Bearingless rotor system.................................................4-4
Belt drive clutch............................................................4-11
Bernoulli's Principle........................................................2-2
Blade span.......................................................................2-6
D
d’Amécourt, Gustave de Ponton.....................................1-1
Decision making models...............................................14-5
Decision-making mrocess.............................................14-4
Density altitude...............................................................7-2
Determining empty weight.............................................6-2
Dissymmetry of lift.......................................................2-22
Downwash.....................................................................2-10
Drag......................................................................... 2-2, 2-5
induced drag................................................................2-6
parasite drag................................................................2-6
profile drag..................................................................2-5
total drag......................................................................2-6
Dynamic rollover........................................................11-12
E
Effective translational lift (ETL)..................................2-20
Effect of weight versus density altitude........................11-9
Elastomeric bearings.......................................................4-5
Electrical systems..........................................................4-14
Emergency Equipment and survival gear...................11-23
Engine fuel control system............................................4-13
Engines............................................................................4-8
reciprocating engine....................................................4-8
turbine engine..............................................................4-8
Engine start and rotor engagement....................... 8-3, 13-8
En route procedures......................................................13-8
Environmental dystems.................................................4-17
F
Fenestron.........................................................................1-4
Flicker vertigo...............................................................13-7
Flight Instruments.........................................................12-2
Flightpath velocity..........................................................2-7
Four fundamentals..........................................................9-2
Freewheeling unit............................................................4-6
Fuel supply system........................................................4-12
Fundamental skills of attitude instrument flying..........12-3
Fuselage..........................................................................4-2
G
General Aviation Manufacturers
Association (GAMA)......................................................5-1
Glass cockpit or advanced avionics aircraft..................12-5
Go-around.....................................................................9-20
Governor/correlator.........................................................3-2
Ground lighting illusions..............................................13-9
Ground reference maneuvers........................................9-14
common errors during ground reference
maneuvers..................................................................9-17
rectangular course.....................................................9-14
s-turns........................................................................9-15
turns around a point...................................................9-16
Ground resonance.......................................................11-11
Gyroscopic precession..................................................2-16
H
Heading control...............................................................3-4
Height/velocity diagram................................................11-8
Helicopter........................................................................1-1
Helicopter control and performance.............................12-3
Helicopter night VFR operations................................13-10
I-2
High and low density altitude conditions........................7-2
Hovering autorotation...................................................2-24
Hovering flight..............................................................2-13
Hovering—forward flight...............................................9-5
Hovering performance....................................................7-3
Hovering—sideward flight..............................................9-6
Hovering turn..................................................................9-4
Hover taxi........................................................................9-7
Hub..................................................................................2-8
Humidity.........................................................................7-2
Hydraulics.....................................................................4-14
I
Illusions leading to landing errors.................................13-9
Induced flow.......................................................... 2-7, 2-20
Induced flow (downwash).............................................2-10
In-ground effect............................................................2-10
Instrument check...........................................................12-2
Intermeshing rotors.........................................................1-4
K
Kaman, Charles H...........................................................1-2
L
Landing—stuck left pedal...........................................11-16
Landing—stuck neutral or right pedal........................11-17
Leading edge...................................................................2-7
Lift...................................................................................2-2
Loading chart method.....................................................6-5
Low-G conditions and mast bumping.........................11-14
Low reconnaissance......................................................10-2
Low rotor RPM and blade stall...................................11-15
LTE at altitude............................................................11-20
M
Main rotor disk interference (285–315°)....................11-19
Main rotor system...........................................................4-2
Main rotor transmission................................................4-10
Maximum gross weight...................................................6-2
Maximum performance takeoff....................................10-2
Mean camber line............................................................2-6
Medium and high frequency vibrations......................11-22
Minimum equipment lists (MELs) and operations
with inoperative equipment.............................................8-2
Moisture..........................................................................7-2
Multi-engine emergency operations...........................11-22
Myopia..........................................................................13-2
N
Newton’s Third Law of Motion......................................2-4
Night flight....................................................................13-7
Night myopia................................................................13-2
Night vision...................................................................13-4
Normal approach to a hover..........................................9-19
Normal approach to the surface....................................9-20
Normal descent.............................................................9-13
Normal takeoff from a hover..........................................9-8
Normal takeoff from the surface.....................................9-9
Normal takeoffs and landings.....................................11-13
NOTAR®........................................................................1-4
O
Obstruction detection....................................................13-6
Out of ground effect......................................................2-10
P
Passengers.......................................................................8-4
PAVE checklist.............................................................14-6
Pendular action..............................................................2-14
Performance charts..........................................................7-2
climb performance.......................................................7-4
hovering performance.................................................7-3
Pilot at the flight controls................................................8-6
Pinnacle and ridgeline operations...............................10-10
Pitch control..................................................................2-16
Powered flight...............................................................2-13
Power failure in a hover................................................11-7
Practice autorotation with a power recovery................11-6
Preflight................................................................. 8-2, 13-7
Presbyopia.....................................................................13-2
R
Ramp attendants and aircraft servicing personnel..........8-4
Rapid deceleration or quick stop...................................10-4
Rearward flight..............................................................2-23
Reciprocating engines...................................................4-13
Reconnaissance procedures..........................................10-2
Recovery from low rotor RPM...................................11-15
Recovery technique.....................................................11-20
Relative-motion illusion................................................13-6
Relative wind.......................................................... 2-7, 2-8
Resultant relative wind........................................... 2-7, 2-8
Retreating blade............................................................2-18
Retreating blade stall...................................................11-11
Reversible perspective illusion.....................................13-6
Rigid rotor system...........................................................4-3
Rods..............................................................................13-4
Root.................................................................................2-8
Rotational relative wind (tip path plane)........................2-8
Rotor configurations........................................................1-4
Rotorcraft........................................................................1-1
Rotorcraft Flight Manual (RFM)....................................5-1
aircraft and systems description..................................5-5
emergency procedures.................................................5-4
general information.....................................................5-2
handling, servicing, and maintenance.........................5-5
normal procedures.......................................................5-5
operating limitations....................................................5-2
airspeed....................................................................5-2
altitude.....................................................................5-3
flight.........................................................................5-4
placards....................................................................5-4
powerplant...............................................................5-3
rotor..........................................................................5-3
weight and loading distribution...............................5-3
performance.................................................................5-5
preliminary pages........................................................5-2
safety and operational tips...........................................5-6
supplements.................................................................5-6
weight and balance......................................................5-5
Rotor safety considerations.............................................8-3
Rotor system...................................................................1-3
Running/rolling takeoff.................................................10-3
S
Settling With Power (Vortex Ring State).....................11-9
Shallow approach and running/roll-on landing.............10-6
Sideward flight..............................................................2-22
Sikorsky, Igor..................................................................1-2
Single-engine failure...................................................11-22
Skids..............................................................................9-12
Slips..............................................................................9-12
Slope takeoff.................................................................10-8
Slope takeoffs and landings........................................11-13
Stability augmentations systems...................................4-16
Straight-and-level flight...................................... 9-10, 12-4
Structural design...........................................................4-11
Swash plate assembly.....................................................4-6
Synchropter.....................................................................1-4
System malfunctions...................................................11-16
T
Tail rotor.........................................................................1-5
Tail Rotor vortex ring state (210–330°)......................11-20
Takeoff........................................................................10-10
Tandem rotor........................................................... 1-3, 4-6
Taxiing............................................................................9-7
Taxi technique...............................................................13-8
The effect of weight versus density altitude.................11-9
The four fundamentals....................................................9-2
Throttle............................................................................1-6
Throttle control...............................................................3-2
Thrust...................................................................... 2-2, 2-5
I-3
Tip...................................................................................2-8
Traffic patterns..............................................................9-17
Trailing edge...................................................................2-7
Translating tendency or drift.........................................2-14
Translational lift............................................................2-19
Transmission system.....................................................4-10
Transverse flow effect...................................................2-22
Turbine............................................................................4-9
Turbine age.....................................................................1-2
Turbine engines.............................................................4-14
Turning flight................................................................2-23
Turns.............................................................................9-11
Twist...............................................................................2-8
U
Unanticipated yaw/loss of tail rotor
effectiveness (LTE).....................................................11-17
Use of collective.........................................................11-13
V
Venturi effect..................................................................2-3
Venturi flow....................................................................2-3
Vertical flight................................................................2-17
Vertical speed indicator................................................12-2
Vertical takeoff to a hover..............................................9-3
Vision in flight..............................................................13-2
Visual acuity.................................................................13-3
Visual deficiencies........................................................13-2
W
Weathercock stability (120-240°)...............................11-20
Weight.......................................................2-2, 2-4, 6-2, 7-2
Weight and balance calculations.....................................6-3
Winds..............................................................................7-2
I-4